Restructure to multi-source architecture; fix GitHub repo timeline filter

- Rename package launchpad_weekly_activity -> weekly_activity
- Split into model.py (ActivityReport, Section), report.py (source-agnostic
  formatter), cli.py (subcommand dispatch), sources/ (per-source modules)
- Move Launchpad code to sources/launchpad.py implementing ActivitySource
- Add GitHub source (sources/github.py) using httpx: PRs, issues, repos, commits
- Fix GitHub 'Repositories modified' filtering on pushed_at not updated_at
  (metadata changes were showing stale repos with no recent code pushes)
- Add --credentials-file for Launchpad OAuth (bypass keyring for headless)
- Add keyring dep (launchpadlib optional dep; bare import crashes without it)
- Graceful per-query error handling: degraded sections + concise warnings
- Rolling 7-day window (was previous calendar week)

pyproject.toml

@@ -1,12 +1,12 @@
 [project]
-name = "launchpad-weekly-activity"
-version = "0.1.0"
-description = "Weekly Launchpad activity report (merge proposals, branches, bugs) for a user."
+name = "weekly-activity"
+version = "0.2.0"
+description = "Weekly activity report (merge proposals, pull requests, bugs, issues) for Launchpad and GitHub."
 requires-python = ">=3.11"
-dependencies = ["launchpadlib>=2.1.0", "keyring>=25"]
+dependencies = ["launchpadlib>=2.1.0", "keyring>=25", "httpx>=0.27"]
 
 [project.scripts]
-launchpad-weekly-activity = "launchpad_weekly_activity.cli:main"
+weekly-activity = "weekly_activity.cli:main"
 
 [build-system]
 requires = ["hatchling"]
@@ -16,7 +16,7 @@ build-backend = "hatchling.build"
 dev = ["ruff>=0.6", "ty>=0.0.1"]
 
 [tool.hatch.build.targets.wheel]
-packages = ["src/launchpad_weekly_activity"]
+packages = ["src/weekly_activity"]
 
 [tool.ruff]
 target-version = "py311"