docs: update documentation for P7 web UI dashboard completion

- README: add Web UI Dashboard section, update features list with all
  current capabilities (multi-channel, media pipeline, sandboxing, etc.),
  expand model providers table, update architecture diagram
- CHANGELOG: add P7 entries (dashboard SPA, 4 new gateway handlers)
- state.json: add P7 entry with all 6 phases and file lists, update
  overall_progress to reflect P0-P7 completion
- web-ui-dashboard.md: mark as completed with detailed phase outcomes

CHANGELOG.md

@@ -6,6 +6,18 @@ All notable changes to Flynn are documented in this file.
 
 ### Added
 
+- **Web UI Dashboard (P7)** -- Full SPA control dashboard at the gateway web UI with
+  four pages: Dashboard (health stats, channels, auto-refresh), Chat (session selector,
+  streaming tool events, markdown rendering), Sessions (list, history viewer, delete),
+  and Settings (hook pattern editor, tool list, config viewer). No build step — vanilla
+  JS with ES modules, hash-based routing, and WebSocket JSON-RPC client with auto-reconnect.
+- **Gateway: sessions.delete** -- New handler to clear a session's message history
+- **Gateway: sessions.switch** -- New handler to switch a WebSocket connection to a
+  different session
+- **Gateway: system.channels** -- New handler listing active channel adapters and their
+  connection status
+- **Gateway: system.usage** -- New handler returning aggregated usage stats (uptime,
+  sessions, connections, tools)
 - **CLI Surface** -- Full command-line interface via `flynn` binary with 6 commands:
   `start`, `tui`, `send`, `sessions`, `doctor`, `config`
 - **Doctor Diagnostics** -- `flynn doctor` validates config, YAML parsing, schema,
@@ -20,10 +32,12 @@ All notable changes to Flynn are documented in this file.
 
 ### Changed
 
+- **Gateway Server** -- `GatewayServerConfig` now accepts `channelRegistry` for
+  channel status reporting; static file server supports `.mjs`, `.png`, `.ico`, `.woff2`
 - **Entry Points Refactored** -- `src/index.ts` and `src/tui.ts` now delegate to
   the CLI module (`src/cli/index.ts`) instead of directly starting the daemon/TUI
 - **Daemon Wiring** -- CronScheduler auto-registers in the channel registry when
-  `automation.cron` jobs are configured
+  `automation.cron` jobs are configured; channelRegistry passed to GatewayServer
 
 ## [0.1.0] - 2026-02-05