feat(web): customizable placeholder, footer text, and color theme via BOR_* env vars

BOR_INPUT_PLACEHOLDER / BOR_FOOTER_TEXT / BOR_THEME (+ the indigo.css example theme); authoring guide: frontend/assets/themes/README.md, docs: README 'Customizing the look'.

tests/unit/test_frontend_brand.py

@@ -95,6 +95,60 @@ def test_brand_js_reskins_title_brand_text_prose_and_attributes() -> None:
         assert marker in js, f"the attribute pass must cover {marker}"
 
 
+def test_brand_js_applies_phase_62_customization_from_the_same_fetch() -> None:
+    """Phase 62 (owner-locked 2026-09-01, TODO L3): the SAME settled
+    /api/config answer also drives the three customization keys — the
+    #message-input placeholder, every .footer-text node, and the theme
+    stylesheet link (inserted right after the styles.css link, guarded
+    by #theme-override, degrading with a console.warn on 404 — A5).
+    No second network call: the keys ride the existing boot fetch."""
+    js = _text(BRAND_JS)
+    assert js.count('= fetch("/api/config"') == 1, (
+        "the three keys must ride the existing boot fetch — no new call"
+    )
+    # 5. The composer placeholder (chat page only — the null guard
+    #    no-ops on every other page).
+    assert 'document.querySelector("#message-input")' in js
+    assert "input_placeholder" in js
+    # 6. The footer line on all 9 pages (the phase-61 hook) — via
+    #    textContent: an operator string can't inject markup.
+    assert 'document.querySelectorAll(".footer-text")' in js
+    assert "footer_text" in js
+    # 7. The theme link: /assets/themes/<name>, inserted right after
+    #    the styles.css link, tagged #theme-override (the idempotency
+    #    guard), with the A5 degradation warn.
+    assert '"/assets/themes/"' in js
+    assert 'link.id = "theme-override"' in js
+    assert 'getElementById("theme-override")' in js
+    assert 'insertAdjacentElement("afterend", link)' in js
+    assert "link.onerror" in js
+    assert '"brand: theme " + themeName' in js
+    # The styles.css finder must survive the phase-33/54 cache-bust
+    # rewrite: the SERVED HTML carries the asset ref with a
+    # ?v=<token> query (and el.href is the absolute URL), so the match
+    # has to run on the RAW attribute path with query/fragment
+    # stripped — el.href.endsWith(…) would silently skip the insertion
+    # (the theme never applied; found by the task-05 E2E).
+    assert 'getAttribute("href")' in js
+    assert "split(/[?#]/)[0]" in js
+    assert 'endsWith("styles.css")' in js
+    assert "el.href.endsWith" not in js
+    # The empty-skip no-op contract: each key is guarded before any
+    # DOM write, so an unset deployment stays byte-identical.
+    for guard in ("if (placeholder) {", "if (footerText) {", "if (themeName) {"):
+        assert guard in js, (
+            f"an empty value must skip its application ({guard})"
+        )
+    # Independence: the phase-62 block sits AFTER the app_name passes
+    # in the same .then — never gated by the name.
+    assert js.index("// 4. Attributes:") < js.index("// Phase 62"), (
+        "the customization keys must apply after the app_name block, "
+        "even when the name is the default/empty"
+    )
+    # The app_name literal default pin still holds.
+    assert 'window.BOR_BRAND = "Brain of Reese"' in js
+
+
 def test_page_scripts_keep_the_default_literal_exactly_once() -> None:
     """The fallback literal lives in the page scripts' brand() reads —
     exactly one copy per file (a second copy could drift out of sync)."""