refactor(email): split the email library into seven modules

`emailLibrary/index.js` goes from 11,375 lines to 6,187. What came out:

- `settingsPage.js` (879) — the Email Settings view, its form and controls,
  away/auto-reply including the calendar-event sync, and the display
  preferences. The inline-image preference lives here rather than with the
  renderer because the settings form owns writing it.
- `unsubscribe.js` (1,224) — the bulk-unsubscribe review flow. One exported
  entry point, its own localStorage keys, its own agent-tool-output listeners.
- `reader.js` (676) — opening an email as a docked tab or a floating window,
  plus the AI summary panel both of them share.
- `menus.js` (855) — the reader More menu, the card kebab menu, the bulk
  Actions menu and `_bulkAction`.
- `bodyRender.js` (871) — plain and threaded body rendering, inline MIME
  images, quote folding.
- `attachments.js` (491) — attachment chips and the deferred load for messages
  whose attachment list was not in the list response.
- `aiReply.js` (449) — AI-reply entry points, the per-message context draft,
  the translate and remind submenus.

The extracted modules import back from `index.js`, so the graph has cycles.
That is safe for hoisted function declarations and unsafe for a value read
during evaluation, so nothing crosses a module boundary except functions:
`API_BASE` is re-declared per module, the way `emailInbox.js` and
`emailShared.js` already do it, and `_autoReplyRefreshSeq` moves into
`state.js` because the settings page and the unread-badge refresh both write
it and an imported binding is read-only. The module-graph test enters the
package at each module in turn, which is the order that would expose a
dead-zone read.

Two test helpers grew while doing this. `js_function_source` replaces three
marker-pair slices ("from this signature down to that comment") whose end
marker had moved into another module — the slice ran past the function and
kept passing against the wrong text. Its first implementation balanced braces
by walking characters and ended `_toggleCardPreview` 18 lines early, because
the apostrophe in `// that's a scroll, not a nav` opened a string that ate the
braces after it. It now keys on the invariant the file actually holds: a
top-level declaration starts at column 0, so its closing brace is the next
lone `}` at column 0.

tests/test_email_library_prewarm.py

@@ -4,7 +4,7 @@ import shutil
 import subprocess
 
 import pytest
-from tests.helpers.js_modules import email_library_source
+from tests.helpers.js_modules import email_library_source, js_function_source
 
 
 _REPO = Path(__file__).resolve().parents[1]
@@ -14,65 +14,7 @@ def _source() -> str:
 
 
 def _function_source(name: str) -> str:
-    """Return one top-level JS function using balanced braces."""
-    text = _source()
-    markers = (f"function {name}", f"async function {name}", f"export function {name}", f"export async function {name}")
-    starts = [text.find(marker) for marker in markers]
-    starts = [start for start in starts if start >= 0]
-    assert starts, f"missing function {name}"
-    start = min(starts)
-    paren = text.index("(", start)
-    paren_depth = 0
-    quote = None
-    escaped = False
-    for index in range(paren, len(text)):
-        char = text[index]
-        if quote:
-            if escaped:
-                escaped = False
-            elif char == "\\":
-                escaped = True
-            elif char == quote:
-                quote = None
-            continue
-        if char in ("'", '"', "`"):
-            quote = char
-        elif char == "(":
-            paren_depth += 1
-        elif char == ")":
-            paren_depth -= 1
-            if paren_depth == 0:
-                brace = text.index("{", index)
-                break
-    else:
-        raise AssertionError(f"unterminated signature {name}")
-    depth = 0
-    quote = None
-    escaped = False
-    template_depth = 0
-    for index in range(brace, len(text)):
-        char = text[index]
-        if quote:
-            if escaped:
-                escaped = False
-            elif char == "\\":
-                escaped = True
-            elif char == quote and template_depth == 0:
-                quote = None
-            elif quote == "`" and char == "$" and index + 1 < len(text) and text[index + 1] == "{":
-                template_depth += 1
-            elif quote == "`" and char == "}" and template_depth:
-                template_depth -= 1
-            continue
-        if char in ("'", '"', "`"):
-            quote = char
-        elif char == "{":
-            depth += 1
-        elif char == "}":
-            depth -= 1
-            if depth == 0:
-                return text[start:index + 1]
-    raise AssertionError(f"unterminated function {name}")
+    return js_function_source(name, _source())
 
 
 def _run_scheduler_scenario(scenario: str):