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/user_stories/nav-sources-rag-rename.md

@@ -0,0 +1,49 @@
+# Story: Nav rename — "Sources" becomes "RAG", "Git sources" becomes "Sources"
+
+**Phase:** `48_nav_rename_sources` · **E2E:** `tests/e2e/test_nav_rename_sources.py`
+
+## Narrative
+
+As **the admin (owner)**, the two admin-only nav items are confusing:
+"Sources" (the document catalog) and "Git sources" (the source manager)
+read like the same thing. I want the navbar to say **"RAG"** for the
+document catalog page and **"Sources"** for the source manager page, so
+the labels say what each page *is*: RAG = the indexed knowledge base you
+chat against; Sources = where that knowledge comes from.
+
+- **Given** I am signed in as admin, on any of the six pages (chat,
+  sources, git-sources, tuning, document viewer, login)
+- **When** I look at the primary nav
+- **Then** the catalog link (`#nav-sources`, → `/sources.html`) is
+  labeled **"RAG"** and the manager link (`#nav-git-sources`, →
+  `/git-sources.html`) is labeled **"Sources"** — same ids, same hrefs,
+  same order, same admin-only ship-hidden/reveal contract as before.
+
+## Acceptance criteria
+1. All six pages (`frontend/index.html`, `sources.html`,
+   `git-sources.html`, `tuning.html`, `document.html`, `login.html`)
+   carry the swapped label text on `#nav-sources` ("RAG") and
+   `#nav-git-sources` ("Sources"). Element ids, `href`s, `hidden`
+   defaults, `is-active`/`aria-current` markers, and the nav order
+   (Chat, RAG, Sources, Tuning) are unchanged — this is a label-only
+   rename, and `header.js` logic (reveal by id) is untouched.
+2. Anonymous visitors still see neither link (ship-hidden contract
+   unchanged); the admin sees both, as before.
+3. Existing test assertions on the old label text are updated
+   (`test_git_sources_admin.py` nav-link text,
+   `test_mobile_hamburger_nav.py` `LINK_TEXTS`); assertions that are
+   NOT about these two nav items stay untouched (the document viewer's
+   "Sources" back button, the "Sync sources" button label, the
+   `/git-sources.html` page-`<h1>`/`<title>` marker).
+4. Story E2E `tests/e2e/test_nav_rename_sources.py` proves: admin sees
+   "RAG" (→ `/sources.html`) and "Sources" (→ `/git-sources.html`) on
+   all six pages; clicking each lands on the right page with
+   `is-active`; anonymous sees both hidden.
+5. Frontend-only: unit + integration green, `app/` coverage
+   unaffected, ruff + pyright clean, no CDN, one `--no-gpg-sign` commit.
+
+## Playwright Mapping Rule
+`tests/e2e/test_nav_rename_sources.py` — one story, one file, run in
+isolation: the two relabeled nav items' full lifecycle (labels, hrefs,
+admin reveal, anonymous hide, click-navigation with the current-page
+marker) on the shared header, desktop viewport.