docs: deep quality pass — expand 10 thin pages, fix specific issues (#4134)

Developer guide stubs expanded to full documentation:
- trajectory-format.md: 56→233 lines (JSONL format, ShareGPT example,
  normalization rules, reasoning markup, replay code)
- session-storage.md: 66→388 lines (SQLite schema, migration table,
  FTS5 search syntax, lineage queries, Python API examples)
- context-compression-and-caching.md: 72→321 lines (dual compression
  system, config defaults, 4-phase algorithm, before/after example,
  prompt caching mechanics, cache-aware patterns)
- tools-runtime.md: 65→246 lines (registry API, dispatch flow,
  availability checking, error wrapping, approval flow)
- prompt-assembly.md: 89→246 lines (concrete assembled prompt example,
  SOUL.md injection, context file discovery table)

User-facing pages expanded:
- docker.md: 62→224 lines (volumes, env forwarding, docker-compose,
  resource limits, troubleshooting)
- updating.md: 79→167 lines (update behavior, version checking,
  rollback instructions, Nix users)
- skins.md: 80→206 lines (all color/spinner/branding keys, built-in
  skin descriptions, full custom skin YAML template)

Hub pages improved:
- integrations/index.md: 25→82 lines (web search backends table,
  TTS/browser providers, quick config example)
- features/overview.md: added Integrations section with 6 missing links

Specific fixes:
- configuration.md: removed duplicate Gateway Streaming section
- mcp.md: removed internal "PR work" language
- plugins.md: added inline minimal plugin example (self-contained)

13 files changed, ~1700 lines added. Docusaurus build verified clean.

website/docs/getting-started/updating.md

@@ -20,6 +20,43 @@ This pulls the latest code, updates dependencies, and prompts you to configure a
 `hermes update` automatically detects new configuration options and prompts you to add them. If you skipped that prompt, you can manually run `hermes config check` to see missing options, then `hermes config migrate` to interactively add them.
 :::
 
+### What happens during an update
+
+When you run `hermes update`, the following steps occur:
+
+1. **Git pull** — pulls the latest code from the `main` branch and updates submodules
+2. **Dependency install** — runs `uv pip install -e ".[all]"` to pick up new or changed dependencies
+3. **Config migration** — detects new config options added since your version and prompts you to set them
+4. **Gateway auto-restart** — if the gateway service is running (systemd on Linux, launchd on macOS), it is **automatically restarted** after the update completes so the new code takes effect immediately
+
+Expected output looks like:
+
+```
+$ hermes update
+Updating Hermes Agent...
+📥 Pulling latest code...
+Already up to date.  (or: Updating abc1234..def5678)
+📦 Updating dependencies...
+✅ Dependencies updated
+🔍 Checking for new config options...
+✅ Config is up to date  (or: Found 2 new options — running migration...)
+🔄 Restarting gateway service...
+✅ Gateway restarted
+✅ Hermes Agent updated successfully!
+```
+
+### Checking your current version
+
+```bash
+hermes version
+```
+
+Compare against the latest release at the [GitHub releases page](https://github.com/NousResearch/hermes-agent/releases) or check for available updates:
+
+```bash
+hermes update --check
+```
+
 ### Updating from Messaging Platforms
 
 You can also update directly from Telegram, Discord, Slack, or WhatsApp by sending:
@@ -28,7 +65,7 @@ You can also update directly from Telegram, Discord, Slack, or WhatsApp by sendi
 /update
 ```
 
-This pulls the latest code, updates dependencies, and restarts the gateway.
+This pulls the latest code, updates dependencies, and restarts the gateway. The bot will briefly go offline during the restart (typically 5–15 seconds) and then resume.
 
 ### Manual Update
 
@@ -51,6 +88,57 @@ hermes config check
 hermes config migrate   # Interactively add any missing options
 ```
 
+### Rollback instructions
+
+If an update introduces a problem, you can roll back to a previous version:
+
+```bash
+cd /path/to/hermes-agent
+
+# List recent versions
+git log --oneline -10
+
+# Roll back to a specific commit
+git checkout <commit-hash>
+git submodule update --init --recursive
+uv pip install -e ".[all]"
+
+# Restart the gateway if running
+hermes gateway restart
+```
+
+To roll back to a specific release tag:
+
+```bash
+git checkout v0.6.0
+git submodule update --init --recursive
+uv pip install -e ".[all]"
+```
+
+:::warning
+Rolling back may cause config incompatibilities if new options were added. Run `hermes config check` after rolling back and remove any unrecognized options from `config.yaml` if you encounter errors.
+:::
+
+### Note for Nix users
+
+If you installed via Nix flake, updates are managed through the Nix package manager:
+
+```bash
+# Update the flake input
+nix flake update hermes-agent
+
+# Or rebuild with the latest
+nix profile upgrade hermes-agent
+```
+
+Nix installations are immutable — rollback is handled by Nix's generation system:
+
+```bash
+nix profile rollback
+```
+
+See [Nix Setup](./nix-setup.md) for more details.
+
 ---
 
 ## Uninstalling