Timeline's "Open" button (chunks view) and chunk-row clicks (files view)
went to ``showDetailFromChunk`` → Search tab's detail panel. But the
user landing on Search after clicking a Timeline chunk sees an empty
left-side results pane ("Enter a query to search") next to a populated
detail on the right — the panel reads as orphaned. The Source tab
already exposes Copy / Edit / Delete on every chunk (the same
operations Search detail offers), and the two preceding PRs (#673
vendor sub-tab follow-through, #674 Home-recent activation) built the
``_navigateToSource(path)`` plumbing — pending-activate handoff plus
eager vendor resolve — for exactly this kind of cross-tab jump.

Reuses that plumbing from Timeline:

  - ``_navigateToSource`` gains an optional ``chunkId`` argument and
    sets ``STATE.pendingActivateChunkId`` alongside the existing
    ``pendingActivatePath``. Empty-string chunkId means "source-level
    only, no card highlight" — keeps the Home-recent and command-
    palette callers behaving exactly as before.
  - ``browseSource`` consumes ``pendingActivateChunkId`` after
    ``content`` lands in the DOM: queries by ``data-chunk-id``
    (already set on every ``.chunk-card`` since the existing browse
    code path), scrolls into view, expands the accordion if the card
    is collapsible, and pulses a ~1.4s ``.tl-target-flash``. Cleared
    unconditionally so a follow-up Load-All re-render of the same
    source doesn't re-flash an old target.
  - Timeline rewrites three call sites:
      * Chunks view "Open" button → ``_navigateToSource(c.source_file,
        c.id)``. Button label moves from hard-coded "Open" to
        ``timeline.open_in_source`` (en: "Open in source", ko:
        "소스에서 보기").
      * Files view file header gains a small ghost-style
        ``.tl-file-open-source`` button on the right edge that
        ``stopPropagation``'s the row's expand/collapse and navigates
        to the source path (no chunk highlight — file headers don't
        carry a single canonical chunk).
      * Files view per-chunk row click → ``_navigateToSource(c.source
        _file, c.id)``.

``showDetailFromChunk`` is kept: ``app.js:4834`` still uses it for the
Source-chunks side panel inside the Search detail (intra-detail "jump
to a sibling chunk in the same source"), which is a different flow.
The Timeline call sites are the only ones changing.

Cache-bust: ``style.css?v=72→v=73``, ``app.js?v=87→v=88``,
``timeline.js?v=1→v=2`` per ``feedback_static_asset_cache_bust.md`` —
all three files have body changes.

i18n parity verified by ``test_i18n.py`` (12 passed); ruff +
ruff-format clean. Manual verification with Playwright MCP against a
live ``mm web`` against the developer's real DB:

  - Chunks-view "Open in source" → tab=sources, exactly one
    ``.chunk-card.tl-target-flash`` on the matching ``data-chunk-id``,
    flash visible ~205ms after click then auto-removed.
  - Files-view header button → tab=sources, no chunk flash (intended).
  - Files-view header non-button click → expand/collapse only, tab
    unchanged. ``stopPropagation`` on the new button confirmed.
  - KO label "소스에서 보기" rendered on first paint (``data-i18n``
    + langchange wiring already covers this since PR #587).

Co-Authored-By: Claude <[email protected]>