docs: README screenshot refresh + full markdown sweep (v0.34.3, 433 tests, Sprint 26 completed)

* Revise images and enhance layout description in README

Updated images and added new content to the layout section.

* docs: markdown sweep -- v0.34.3, 433 tests, Sprint 26 completed, custom themes row restored

- THEMES.md: restore custom themes row removed by PR #105
- ROADMAP.md: bump version/tests to v0.34.3/433; mark themes [x]; add v0.34/v0.34.1/v0.34.2/v0.34.3 to sprint history table
- SPRINTS.md: Sprint 26 marked COMPLETED; version bumped to v0.34.3; horizon sprint updated to Sprint 25 (Desktop)
- TESTING.md: coverage updated to Sprint 26 / v0.34.3; test count corrected to 433; port corrected to 8786

---------

Co-authored-by: Nathan Esquenazi <nesquena@gmail.com>

ROADMAP.md

@@ -3,8 +3,8 @@
 > 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: v0.33 (April 5, 2026)
-> Tests: 424 total (424 passing, 0 failures)
+> Last updated: v0.34.3 (April 5, 2026)
+> Tests: 433 total (433 passing, 0 failures)
 > Source: <repo>/
 
 ---
@@ -42,6 +42,10 @@
 | Sprint 23 | Agentic transparency | Token/cost display, subagent cards, skill picker in cron, skill linked files, workspace tree persistence, timestamp fixes | 424 |
 | v0.32 | Auto-compaction handling | Compression detection, /compact command, real context window indicator | 424 |
 | v0.33 | /insights sync | Opt-in state.db sync so `hermes /insights` includes WebUI sessions | 424 |
+| v0.34 | Sprint 26 — Pluggable themes | Dark, Light, Slate, Solarized, Monokai, Nord; settings unsaved-changes guard; /theme command | 433 |
+| v0.34.1 | Theme variable polish | 30+ hardcoded dark-navy colors replaced with theme-aware CSS variables | 433 |
+| v0.34.2 | Theme text colors | 5 new per-theme typography variables (--strong, --em, --code-text, --code-inline-bg, --pre-text) | 433 |
+| v0.34.3 | Light theme final polish | 46 light-scoped selector overrides for sidebar, roles, chips, interactive elements | 433 |
 
 ---
 
@@ -209,7 +213,7 @@
 - [x] Background task cancel (activity bar Cancel button)
 - [ ] Code execution cell (deferred)
 - [ ] Desktop application (Sprint 25, PLANNED)
-- [ ] Pluggable UI themes -- light, dark, Solarized, Monokai, Nord (Sprint 26, PLANNED)
+- [x] Pluggable UI themes -- Dark, Light, Slate, Solarized, Monokai, Nord (Sprint 26, v0.34)
 - [ ] Extended slash command / skill integration (deferred)
 - [ ] Virtual scroll for large lists (deferred)