feat(ui): rename nav items — "Sources" becomes "RAG", "Git sources" becomes "Sources"

Owner request (2026-08-28): the two admin-only nav items read like the
same thing, so they are relabeled — the document-catalog link
(#nav-sources, /sources.html) becomes "RAG" and the source-manager link
(#nav-git-sources, /git-sources.html) becomes "Sources".

Phase 48 (48_nav_rename_sources), label-only per the locked decision:
- all six pages (index, sources, git-sources, tuning, document, login):
  the two <a> texts swap; ids, hrefs, hidden defaults, is-active /
  aria-current placement, and nav order (Chat, RAG, Sources, Tuning)
  are byte-unchanged otherwise.
- header.js: comment/docstring label mentions only — the reveal-by-id
  logic is untouched (ship-hidden/reveal contract intact).
- test_git_sources_admin.py / test_mobile_hamburger_nav.py: the two
  suites that asserted the old label text are updated; comment-only
  label fixes in test_shared_header.py / test_nav_consistency.py.
- tests/e2e/test_nav_rename_sources.py: the story E2E (green in
  isolation) — renamed labels + unchanged hrefs/order/markers on all
  six pages, click navigation with the active marker, the anonymous
  ship-hidden contract, and regression guards for the untouched
  controls (#sync-label "Sync sources", viewer #doc-back "Sources").
- All eight surrounding header/nav suites stay green in isolation;
  unit+integration green, app/ coverage 99% (frontend-only change),
  ruff + pyright clean.

Note: per this phase file-level staging, the six page files and
header.js also carry the same-day in-flight owner rework that was
already in the working tree when phase 48 ran (mobile sign-in dropdown
copy, sync button ship-hidden on the Sources page); the label rename
itself is the two-text swap on each page.

.agent/phases/complete/48_nav_rename_sources/00_phase.md

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+# Phase 48 — Nav rename: "Sources" → "RAG", "Git sources" → "Sources"
+
+**Source:** owner request (chat, 2026-08-28) — "The 'Git sources' navbar item should be renamed to 'Sources' and the 'Sources' navbar item should be renamed to 'RAG'."
+**Story:** `.agent/user_stories/nav-sources-rag-rename.md`
+**Context:** the shared header (phase 19, `frontend/assets/header.js`) ships ONE nav on all six pages — `[Chat, #nav-sources "Sources" → /sources.html, #nav-git-sources "Git sources" → /git-sources.html, #nav-tuning "Tuning"]` — with the two admin-only links ship-hidden and revealed by id once `/api/whoami` says admin (phase 16 contract, phase 34 same-header-everywhere, phase 46 mobile hamburger). Both labels are plain `<a>` text in the six page files; `header.js` toggles only the `hidden` attribute and never reads the label, so the rename is markup-only.
+
+## Objective
+Relabel the two admin-only nav items across all six pages — the document-catalog link (`#nav-sources`) becomes **"RAG"** and the source-manager link (`#nav-git-sources`) becomes **"Sources"** — with ids, hrefs, order, the ship-hidden/reveal contract, and every other page control (viewer back button, Sync button, page titles/h1s) unchanged.
+
+## Dependencies
+- `34_consistent_navbar` / `19_shared_header` (complete) — the same full header block on all six pages and the `header.js` reveal-by-id contract this phase preserves.
+- `35_git_sources_admin` (complete) — the `#nav-git-sources` link (and the `/git-sources.html` page) it labels.
+- `46_mobile_hamburger_nav` (complete) — the `LINK_TEXTS` assertion in `test_mobile_hamburger_nav.py` that this phase updates.
+
+## Tasks
+1. `01_nav_label_swap.md` — swap the two label texts in all six page files + the label mentions in `header.js`'s docstring/comments (no logic).
+2. `02_existing_test_labels.md` — update the two test suites that assert the old label text; leave every other assertion (viewer back button, sync label, h1/title markers) untouched.
+3. `03_story_e2e_regression_commit.md` — the story E2E (`test_nav_rename_sources.py`), the regression suites in isolation, ruff + pyright, the one `--no-gpg-sign` commit, and the phase-dir move.
+
+## Testing & Quality
+- Unit/integration: no new backend logic (frontend markup only). The existing no-CDN integration test (`tests/integration/test_api.py::test_html_pages_served_locally_no_cdn`) must still pass — the swap touches no tags or origins (the `/git-sources.html` "Git sources" marker keeps matching the page's unchanged `<h1>`).
+- Coverage: frontend-only; the `app/` >90% gate is unaffected (unchanged).
+- E2E (mandatory, A16): `tests/e2e/test_nav_rename_sources.py` — the story gate, run in isolation.
+
+## Completion Criteria
+- [ ] All six pages show **"RAG"** on `#nav-sources` (href `/sources.html`) and **"Sources"** on `#nav-git-sources` (href `/git-sources.html`); nav order and `is-active`/`aria-current` placement unchanged; no id/href/`hidden` change.
+- [ ] Anonymous still sees neither link; the admin sees both (contract preserved, proven by the story E2E + `test_shared_header.py`).
+- [ ] `uv run pytest` green (the two updated suites included); `uv run pytest --cov=app --cov-report=term-missing` TOTAL unchanged (no backend change).
+- [ ] Regression E2E suites green in isolation: `test_nav_consistency.py`, `test_shared_header.py`, `test_mobile_hamburger_nav.py`, `test_git_sources_admin.py`, `test_header_consistency.py`, `test_sources_midstream_bug.py`, `test_smoke.py`.
+- [ ] `uv run pytest tests/e2e/test_nav_rename_sources.py -v --no-cov` green in isolation.
+- [ ] `uv run ruff check . && uv run pyright` clean (no Python behavior change, but run the gate).
+- [ ] UI Structure Check (AGENTS.md rule 5): labeled links, landmarks/contrast/focus unchanged; no CDN (rule 6).
+- [ ] One `--no-gpg-sign` commit staging only this phase's files; `.agent/phases/todo/48_nav_rename_sources/` moved to `.agent/phases/complete/`.
+
+## Locked decisions
+- **Label-only rename (owner request 2026-08-28)** — exactly the two nav item texts change. Element ids (`#nav-sources`, `#nav-git-sources`), hrefs, nav order, the ship-hidden/reveal contract, `header.js` behavior, and every other label (the document viewer's "Sources" back button, the "Sync sources" button, page `<title>`/`<h1>` — incl. "Knowledge base" and "Git sources") are OUT of scope. If the owner later wants the page titles/h1s to follow the nav labels, that is a follow-up phase, not this one.
+- **A11 untouched** — vanilla HTML only, no CDN, no new packages, no new tags.
+- **A10 untouched** — no endpoint, auth, or `header.js` logic change; the rename rides the existing reveal-by-id path.
+- **No schema / migration** — purely a markup + test-label change.
+- **A16 / A17 honoured** — one new story E2E suite + one atomic `--no-gpg-sign` commit.