converge: phase 2 — SSE relay client for realtime pull on push

- RepoConfig gains rcGiteaRepo :: Maybe Text for relay matching
- Options gains optRelayUrl :: Maybe Text (--relay-url CLI, relay_url config)
- connectRelay connects to converge-relay SSE endpoint, parses push events,
  triggers gitPull on matching repos (by gitea_repo + branch)
- Exponential backoff reconnection (1s .. 60s) on disconnect/error
- Skips pull if repo is mid-operation (merge/rebase/etc.)
- Dependencies: http-client, http-client-tls, http-types, aeson, bytestring
- SSE parser handles event:/data: fields, blank-line delimiters, CRLF endings
- Updated SPEC.md, example config, and help text

converge.example.yaml

@@ -2,14 +2,18 @@
 # Place at ~/.config/converge/config.yaml to use by default,
 # or pass explicitly with: converge --config converge.yaml
 
+# relay_url: "http://localhost:8080/events"  # converge-relay SSE endpoint for realtime push notifications
+
 repos:
   - path: /home/jbrechtel/org
     remote: origin
     branch: main
+    # gitea_repo: "myorg/org-repo"    # Gitea repository full_name for relay matching
     # notify_on_pull: true  # send a notification when new commits are pulled
   - path: /work/personal/hawat
     # remote defaults to "origin"
     # branch defaults to "main"
+    # gitea_repo: "myorg/hawat"
 
 # debounce_ms: 5000   # optional, defaults to 5000