docs: update all markdown files to reflect v0.18 state

Brings all documentation up to date after Sprint 16, PRs #18-25:

- CHANGELOG: add v0.18 (Sprint 16), v0.17.3 (bug fixes), update footer
- ROADMAP: Sprint 16 in history, custom model discovery feature, updated
  line counts and architecture table, fix Wave 3 checkboxes
- SPRINTS: bump version to v0.18, update parity percentages, fix
  reasoning display sprint reference
- ARCHITECTURE: update all file line counts to match current source,
  add Session model fields (pinned, archived, project_id, tool_calls),
  document ICONS constant and sessions.js overlay pattern, update
  Phase A/I sections
- BUGS: restructure with open/fixed sections, add v0.17.3 fixes

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

BUGS.md

@@ -1,18 +1,40 @@
 # Bugs Backlog
 
-This file tracks UI bugs and polish items to address in a future sprint.
+This file tracks UI bugs and polish items. Fixed items are kept for reference.
 
-## ~~Conversation list title truncation / hover actions~~ — Fixed (Sprint 16)
+---
+
+## Open Bugs
+
+*No open bugs at this time.*
+
+---
+
+## Fixed
+
+### ~~Session title truncation / hover actions~~ -- Fixed (Sprint 16)
 
 - **Was:** Action icons reserved ~30px of space even when invisible, truncating titles.
 - **Fix:** Wrapped all action buttons in a `.session-actions` overlay container with `position:absolute`. Titles now use full available width. Actions appear on hover with a gradient fade from the right edge.
 
-## ~~Folder/project assignment interaction feels sticky~~ — Fixed (Sprint 16)
+### ~~Folder/project assignment interaction feels sticky~~ -- Fixed (Sprint 16)
 
 - **Was:** Folder icon stayed permanently visible (blue, 60% opacity) when a session belonged to a project.
 - **Fix:** Replaced `.has-project` persistent button with a colored left border matching the project color. The folder button now only appears in the hover overlay like all other actions.
 
+### ~~Project picker clipping and width~~ -- Fixed (v0.17.3)
+
+- **Was:** Picker was clipped by `overflow:hidden` on `.session-item` ancestors. With `position:fixed`, no containing block constrained width -- picker stretched to full viewport.
+- **Fix:** Dynamic width calculation (min 160px, max 220px). Event listener reordering. Cleanup sequence corrected. (PR #25)
+
+### ~~NameError crash in model discovery~~ -- Fixed (v0.17.3)
+
+- **Was:** `logger.debug()` called in custom endpoint `except` block, but `logger` was never imported in `config.py`. Every failed endpoint fetch crashed with `NameError`.
+- **Fix:** Replaced with silent `pass` -- unreachable endpoints are expected when no local LLM is configured. (PR #24)
+
+---
+
 ## Notes
 
-- Both issues resolved in Sprint 16 (Session Sidebar Visual Polish).
-- Icons replaced from inconsistent emoji HTML entities to monochrome SVG line icons.
+- Sprint 16 replaced all emoji HTML entities with monochrome SVG line icons (`ICONS` constant in `sessions.js`).
+- All session action buttons now use the overlay pattern for consistent UX.