feat: add WebVTT context generation to chat WebSocket endpoint

- Import topics_to_webvtt_named and recordings controller
- Add _get_is_multitrack helper function
- Generate WebVTT context on WebSocket connection
- Add get_context message type to retrieve WebVTT
- Maintain backward compatibility with echo for other messages
- Add test fixture and test for WebVTT context generation

Implements task fn-1.2: WebVTT context generation for transcript chat

.flow/usage.md

@@ -0,0 +1,76 @@
+# Flow-Next Usage Guide
+
+Task tracking for AI agents. All state lives in `.flow/`.
+
+## CLI
+
+```bash
+.flow/bin/flowctl --help              # All commands
+.flow/bin/flowctl <cmd> --help        # Command help
+```
+
+## File Structure
+
+```
+.flow/
+├── bin/flowctl         # CLI (this install)
+├── epics/fn-N.json     # Epic metadata
+├── specs/fn-N.md       # Epic specifications
+├── tasks/fn-N.M.json   # Task metadata
+├── tasks/fn-N.M.md     # Task specifications
+├── memory/             # Context memory
+└── meta.json           # Project metadata
+```
+
+## IDs
+
+- Epics: `fn-N` (e.g., fn-1, fn-2)
+- Tasks: `fn-N.M` (e.g., fn-1.1, fn-1.2)
+
+## Common Commands
+
+```bash
+# List
+.flow/bin/flowctl list               # All epics + tasks grouped
+.flow/bin/flowctl epics              # All epics with progress
+.flow/bin/flowctl tasks              # All tasks
+.flow/bin/flowctl tasks --epic fn-1  # Tasks for epic
+.flow/bin/flowctl tasks --status todo # Filter by status
+
+# View
+.flow/bin/flowctl show fn-1          # Epic with all tasks
+.flow/bin/flowctl show fn-1.2        # Single task
+.flow/bin/flowctl cat fn-1           # Epic spec (markdown)
+.flow/bin/flowctl cat fn-1.2         # Task spec (markdown)
+
+# Status
+.flow/bin/flowctl ready --epic fn-1  # What's ready to work on
+.flow/bin/flowctl validate --all     # Check structure
+
+# Create
+.flow/bin/flowctl epic create --title "..."
+.flow/bin/flowctl task create --epic fn-1 --title "..."
+
+# Work
+.flow/bin/flowctl start fn-1.2       # Claim task
+.flow/bin/flowctl done fn-1.2 --summary-file s.md --evidence-json e.json
+```
+
+## Workflow
+
+1. `.flow/bin/flowctl epics` - list all epics
+2. `.flow/bin/flowctl ready --epic fn-N` - find available tasks
+3. `.flow/bin/flowctl start fn-N.M` - claim task
+4. Implement the task
+5. `.flow/bin/flowctl done fn-N.M --summary-file ... --evidence-json ...` - complete
+
+## Evidence JSON Format
+
+```json
+{"commits": ["abc123"], "tests": ["npm test"], "prs": []}
+```
+
+## More Info
+
+- Human docs: https://github.com/gmickel/gmickel-claude-marketplace/blob/main/plugins/flow-next/docs/flowctl.md
+- CLI reference: `.flow/bin/flowctl --help`