feat: Sprint 16 — session sidebar visual polish

- Action buttons overlay: wrap pin/move/archive/dup/trash in a
  .session-actions container with position:absolute. Titles now use
  full available width. Actions appear on hover with gradient fade
  from the right edge. Overlay auto-hides during inline rename.

- SVG line icons: replace all emoji HTML entities with monochrome
  SVGs that inherit currentColor. Consistent across all platforms.

- Pin indicator: small gold star rendered inline only when pinned.
  Unpinned sessions get full title width (zero space reservation).

- Project border: sessions assigned to a project show a colored
  left border matching the project color, replacing the old
  always-visible blue folder button.

Fixes both BUGS.md items (title truncation + sticky folder button).
Tests: 214 passed, 23 pre-existing failures, 0 regressions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ROADMAP.md

@@ -3,7 +3,7 @@
 > Goal: Full 1:1 parity with the Hermes CLI experience via a clean dark web UI.
 > Everything you can do from the CLI terminal, you can do from this UI.
 >
-> Last updated: Sprint 15 (April 1, 2026)
+> Last updated: Sprint 15 / v0.17.1 (April 2, 2026)
 > Tests: 237 passing
 > Source: <repo>/