feat(web): render tool evidence and preview session artifacts

[SSK988I]

Problem

Closes #345. Tool output is difficult to review as generic text, and local artifact links cannot use ordinary Web navigation to reach authenticated files. Includes the controlled artifact access and revision-following slice requested in the maintainer's comments:

• feat(web): add purpose-built renderers for file, diff, test, and terminal evidence #345 (comment)
• feat(web): add purpose-built renderers for file, diff, test, and terminal evidence #345 (comment)

Value

Users can inspect file contents, additions/deletions, test observations and terminal receipts, then open/download a generated report and see its next version after modification. Presentation stays tied to observed tool results rather than a success label.

Approach

• Add bounded specialized read/write/edit/test/terminal cards with sanitized raw fallback and stable live-tool projections across snapshots and replay. Keep unknown tools on the generic path.
• Capture write comparisons inside Pi's native file mutation queue using its pluggable operations. Preserve native write schema, cancellation and success behavior; distinguish creation, overwrite and unchanged content. Limit comparison input to 32 KiB / 1000 lines per file and retained diff to 12 KiB / 300 lines. Unavailable comparison does not turn a successful write into a failure.
• Resolve authenticated local Markdown links through Session/workspace-scoped, read-only artifact handles. Reject out-of-scope paths and symlink/junction traversal; bound reads and grants; keep credentials out of links.
• Show source, revision, text/Markdown preview and bounded download. Resolve nested links relative to the artifact directory. Poll only while a preview is open, retain explicitly stale content on failure, and release access on close/Session transition. Downloads reject changed revisions.
• Rebuild tracked Web assets after merging current main. No development document, private Session data, screenshots or logs are included.

Validation

Final merged revision: 943d13d (includes main 0d17f45). Validation is not fully green:

• bun run check: passes in a clean LF export of the final commit. The Windows working checkout fails format checking on existing CRLF files; no repository-wide line-ending rewrite was made.
• All frontend .spec.ts files through the repository's Vitest runner: 10 files / 132 tests passed after the merge.
• bun run test:web:e2e: 11 passed / 1 failed after the merge. The new artifact scenario passes, using real Pi read/write/edit operations and the real Host with fixture model responses. The failing upstream workspace-selection test computes workspaceName with canonicalWorkspace.split("/"), leaving a full backslash-separated Windows path and timing out finding the menu item (tests/web/openpi-web.e2e.ts:805-816). It is unchanged by this PR. Before the upstream merge, all 10 browser tests passed.
• bun run test: latest parallel Node phase 1370 passed / 2 failed / 9 skipped, then the runner stopped before the serial/frontend phases. Failures were the existing setup integration child-process timeout and detached-workflow settlement timeout. Both files passed isolated earlier. An earlier full run also hung after background-terminal manager assertions completed; owned test processes were stopped and remaining tests run separately. No claim of a complete passing full-suite run.
• Added protocol, artifact authorization/revision, write creation/overwrite/unchanged/failure/cancellation/concurrency, component, accessibility and browser coverage. Focused write/projection tests passed.
• User manually confirmed write creation, overwrite, unchanged content and persistence after refresh, plus opening the Markdown report with a space in its filename. Model-driven report updates/download/stale preview paths have automated browser coverage; no paid-provider automated smoke was run.
• git diff --check: passed.

Impact

• User-visible: evidence cards and read-only artifact previews/downloads. Images/PDF have download fallback; HTML is text, not executable preview. Downloads are capped at 20 MiB. Shell mutations remain terminal evidence and do not invent file diffs.
• Model-facing: no new tool name or preference. Web's native-schema write implementation adds bounded result details; its ordinary textual response is preserved.
• Runtime/lifecycle: in-memory bounded handles, authenticated reads, preview polling cleanup, live-tool cache and native-queue write comparison capture. No external watcher service or file editor.
• Persisted data/config: new write results contain bounded comparison metadata; old records cannot reconstruct missing before-images. No setup/config migration or document changes relative to main.
• Compatibility/risks: Pi 0.85.1 APIs; evidence may be unavailable for large/non-text/unreadable/changing files. This does not claim to eliminate all races with external filesystem writers. Existing tests/Windows validation limitations above remain visible for review.