Add config onboarding wizard and aggregated report

- `weekly-activity config`: interactive wizard writing
  ~/.config/weekly-activity.toml (XDG-aware, --config override), one
  section per source, 0600 permissions, tokens never echoed; re-runs show
  current settings and pre-fill defaults
- `weekly-activity report` (and bare invocation): loads enabled sources,
  collects each independently, joins blocks under one header; a failing
  source renders as [skipped: <source> — error] without aborting
- config.py: typed schema, tomllib reader with strict validation,
  hand-formatted TOML writer (stdlib-only, no new dependency)
- aggregate.py: source spec building + failure-isolated collection +
  combined rendering
- README: document config/report usage and config schema
- tests/: 16 stdlib-unittest cases (config round-trip/escaping/validation,
  aggregation mapping/isolation)

tests/test_aggregate.py

@@ -0,0 +1,101 @@
+"""Unit tests for weekly_activity.aggregate — stubbed sources, no network."""
+
+from __future__ import annotations
+
+import os
+import unittest
+from datetime import datetime
+from unittest import mock
+
+from weekly_activity.aggregate import (
+    SourceSpec,
+    build_specs,
+    collect_specs,
+    format_combined,
+)
+from weekly_activity.config import (
+    ActivityConfig,
+    BtsSettings,
+    GithubSettings,
+    GitlabSettings,
+    LaunchpadSettings,
+)
+from weekly_activity.model import ActivityReport, Section
+
+
+class StubSource:
+    def __init__(self, name: str = "stub", *, fail: bool = False) -> None:
+        self.name = name
+        self._fail = fail
+
+    def collect(self, username: str, since: datetime, until: datetime) -> ActivityReport:
+        if self._fail:
+            raise RuntimeError("kaput")
+        return ActivityReport(
+            source=self.name,
+            username=username,
+            since=since,
+            until=until,
+            sections=[Section("Things", ["did a thing"])],
+            warnings=["some query failed"],
+        )
+
+
+def window() -> tuple[datetime, datetime]:
+    return datetime(2026, 8, 19), datetime(2026, 8, 26)
+
+
+class BuildSpecsTest(unittest.TestCase):
+    def test_maps_every_section_in_order(self) -> None:
+        config = ActivityConfig(
+            launchpad=LaunchpadSettings(username="lp"),
+            github=GithubSettings(username="gh"),
+            gitlab=GitlabSettings(username="gl"),
+            bts=BtsSettings(email="bts@mail"),
+        )
+        specs = build_specs(config)
+        self.assertEqual([s.name for s in specs], ["launchpad", "github", "gitlab", "bts"])
+        self.assertEqual([s.username for s in specs], ["lp", "gh", "gl", "bts@mail"])
+
+    def test_disabled_sections_are_skipped(self) -> None:
+        config = ActivityConfig(github=GithubSettings(username="only-one"))
+        self.assertEqual([s.name for s in build_specs(config)], ["github"])
+
+    def test_launchpad_spec_expands_tilde_credentials_file(self) -> None:
+        settings = LaunchpadSettings(
+            username="u", mode="credentials", credentials_file="~/creds.json"
+        )
+        spec = build_specs(ActivityConfig(launchpad=settings))[0]
+        with mock.patch("weekly_activity.aggregate.LaunchpadSource") as fake_source:
+            spec.make()
+        kwargs = fake_source.call_args.kwargs
+        self.assertEqual(kwargs["credentials_file"], os.path.expanduser("~") + "/creds.json")
+        self.assertFalse(kwargs["anonymous"])
+
+
+class CollectAndFormatTest(unittest.TestCase):
+    def test_failure_isolated_per_source(self) -> None:
+        since, until = window()
+        specs = [
+            SourceSpec(name="alpha", username="a", make=lambda: StubSource("alpha")),
+            SourceSpec(name="beta", username="b", make=lambda: StubSource("beta", fail=True)),
+        ]
+        collected = collect_specs(specs, since, until)
+        self.assertIsNotNone(collected[0].report)
+        self.assertIn("RuntimeError: kaput", collected[1].error or "")
+
+        text = format_combined(collected, since, until)
+        self.assertIn("Weekly activity report — 2 source(s)", text)
+        self.assertIn("Activity report — alpha / ~a", text)
+        self.assertIn("[skipped: beta — RuntimeError: kaput]", text)
+
+    def test_warning_surfaced_inside_block(self) -> None:
+        since, until = window()
+        specs = [SourceSpec(name="gamma", username="g", make=lambda: StubSource("gamma"))]
+        text = format_combined(collect_specs(specs, since, until), since, until)
+        self.assertIn("Warnings (partial data — some queries failed):", text)
+        self.assertIn("some query failed", text)
+
+
+if __name__ == "__main__":
+    unittest.main()