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

package.yaml

@@ -29,10 +29,15 @@ ghc-options:
 
 dependencies:
   - base >= 4.7 && < 5
+  - aeson
   - async
+  - bytestring
   - directory
   - filepath
   - fsnotify
+  - http-client
+  - http-client-tls
+  - http-types
   - optparse-applicative
   - process
   - text