feat(reader): add a session reading trail

[oldwinter]

Built a localized Reading Trail that remembers the notes visited earlier in the current tab and makes them one click away from the existing reader action row. I think it is worth merging because wandering through backlinks and Random Wander is one of the garden's best interactions, and this gives readers a quiet, reversible path through that exploration without accounts, long-term tracking, or another network request.

What changed

• keep up to eight safe, unique note paths in sessionStorage, newest first
• show a compact count badge and anchored trail panel with title/path context
• move revisited notes to the front, exclude the current note, and support clear/empty/failure states
• handle Quartz SPA nav, in-place render, full reload, cleanup, and ReadLater panel mutual exclusion
• localize English, Simplified Chinese, and Traditional Chinese labels
• support keyboard focus restoration, Escape, outside dismissal, dark/light, reduced motion, print, long lists, and extreme CJK/path lengths

Validation

• focused tests: 28/28 passed
• tsc --noEmit: passed
• scoped Prettier and git diff --check: passed
• production Quartz build: passed, 314 inputs / 1911 outputs
• real Chromium QA: SPA order/revisit/uniqueness, reload, clear, Escape/focus, ReadLater exclusion, 1280px desktop, 320px mobile, dark/light, reduced motion, long-list scrolling, and extreme text clamping all passed with no page errors
• full suite: 230/231; the sole failure is the existing ThemeSwitcher test importing undeclared jsdom, in unchanged code
• remote checks: all four Netlify checks failed together after about 10 minutes; public deploy 6a8c8e6facc50100081c10cd ended in error with no error message and GitHub exposed zero annotations, so no deployment configuration or credentials were changed

Impact

• 13 focused design, runtime, storage, style, locale, resource-registration, and test files
• no dependency, lockfile, content, config, CI, infrastructure, deployment, analytics, cookie, permission, secret, or external-request changes
• session data is bounded to eight path/title/timestamp entries and disappears with the tab session
• GitHub Issues are disabled for this repository, so there is no linked issue

Rollback

Revert commit c1cdc31a08cb5350cf7570a2a12e3062cba9cb3e. The feature is isolated; removing its script/style registration, locale fields, and storage module restores the prior reader action row. Existing browser session data is inert without the script.

[netlify]

❌ Deploy Preview for aquamarine-salamander-b041fe failed. Why did it fail? →

Name	Link
🔨 Latest commit	c1cdc31
🔍 Latest deploy log	https://app.netlify.com/projects/aquamarine-salamander-b041fe/deploys/6a8c8e6facc50100081c10cd

[oldwinter]

Blocking review at exact head c1cdc31a08cb5350cf7570a2a12e3062cba9cb3e:

1. Keyboard activation can leave Reading Trail and ReadLater simultaneously open with both triggers aria-expanded=true; pointer dismissal masks this because Enter/Space emits no pointerdown.
2. When storage reads succeed but writes fail, each navigation reloads stale storage over the in-memory fallback. New trail entries disappear and a failed Clear can revive old entries.
3. New spacing breaks DESIGN's base-4 rhythm and the panel implementation substantially duplicates ReadLater.

Unblock action: rebase onto current v5, introduce shared disclosure/storage behavior, and add executable DOM tests for keyboard mutual exclusion plus write-only storage failure. Focused tests pass but source-regex lifecycle tests do not cover these paths.