[StudentWeis]

Summary

Propagate repository count failures instead of treating an unreadable count as empty history. Consolidate repetitive updater version-parser tests without changing updater behavior.

Linked Issue

Closes #308

Changes

• Return Result from storage length/emptiness and repository count APIs, and migrate all workspace callers.
• Stop all three retention/ordinary-clear paths before mutation when reading the count fails.
• Add redb fault-injection regressions that verify error propagation, preservation of records and rich-text sidecars, and successful retry.
• Parameterize valid and invalid version tags, retaining prefix, prerelease, and build metadata coverage.
• Leave database permissions unchanged, as requested.

Testing

• scripts/precheck.sh passes locally: completed the equivalent --check --light checks and --check --rust phase, including formatting, resource validation, 83 script tests, dependency checks, workspace Clippy/tests, isolated Linux tray regression, and documentation.
• New / updated tests cover the change: all three injected count-failure cases failed before the fix and pass after it.
• The local mise rtk shim has no configured version; the validation subprocess excluded that shim directory from PATH and used cargo directly. No environment configuration was modified.
• Native macOS/Windows GUI acceptance was not run locally; this change does not alter GUI interactions.

Self-Check

• PR title follows Conventional Commits
• No hardcoded user-facing strings — no visible strings changed
• Errors defined with thiserror — existing repository error type reused
• No unrelated changes mixed in