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Summary

Records GitHub repository/issue/PR/file analysis completions in the central
usage ledger. These calls previously went through
app/services/analysis.py::_run and never produced a UsageRecord, leaving a
gap in the "every LLM call records a ledger row" requirement.

Problem

Issue #366 requires every LLM call to be recorded. Chat, project chat, project
analysis, reviews and tools were instrumented, but the GitHub analysis path
(analysis._run) called the provider directly. GitHub analysis usage was
therefore invisible to the ledger and dashboards.

Solution

• analysis._run now records one UsageRecord after a successful completion,
  with source="analysis", the authenticated user, provider, and model.
• Accounting is best-effort and wrapped so it can never break analysis.
• Anonymous calls and calls outside an app context are not recorded because they
  have no owner.
• complete() returns text only, so token counts are recorded as estimated
  zeroes rather than guessed.
• Added tests/test_analysis_usage_ledger.py proving one row is written with
  the expected source, owner, provider and model.

Validation

• python -m pytest tests/test_analysis_usage_ledger.py tests/test_stellar_analysis_github.py -q — PASS (22 passed)
• python -m pytest tests/test_stellar_analysis.py tests/test_stellar_analysis_extra.py tests/test_stellar_aware_analysis.py -q — PASS (23 passed)
• python -m ruff check app/services/analysis.py tests/test_analysis_usage_ledger.py — PASS
• python -m black --check app/services/analysis.py tests/test_analysis_usage_ledger.py — PASS
• Repo-wide ruff/black remain blocked by the pre-existing malformed
  app/services/invoice_export.py and tests/test_invoice_export.py files from
  feat(billing): export invoices as CSV and PDF with size bounds (#483) #535.

Risk

Adds one ledger write per successful GitHub analysis. The write is best-effort,
so a ledger failure cannot fail the analysis. Token counts for this path are
estimates (zero) until the provider surface exposes usage on complete().

Issue

Closes #366