Handle invalid configuration with concise diagnostics

[rogerchappel]

Summary

• convert unreadable and malformed .clipcase.json failures into concise ClipcaseError diagnostics
• validate the configuration object and optional string storageDir before path handling
• cover CLI exit messages, stack-trace suppression, and relative/absolute path resolution
• document the accepted shape and recovery steps

Commits

• 4e091e8 test: cover invalid configuration diagnostics
• d922317 fix: validate local configuration
• 51a6324 docs: describe configuration recovery

Verification

• npm ci --ignore-scripts --no-audit --no-fund
• npm run release:check (24 tests, typecheck, build, smoke, packed-package smoke, release contract)
• bash scripts/validate.sh
• git diff --check origin/main...HEAD

All authors and committers verified as Roger Chappel <miscanalysis@gmail.com>.

[rogerchappel]

Automated merge note

Triage class: auto-merge

Summary: Adds concise diagnostics for malformed, unreadable, and wrongly shaped ClipCase configuration, with CLI/unit regressions and storage documentation (5 files, +32/-4).

Checks run: CI test (20/22/24) COMPLETED/SUCCESS; isolated npm ci; npm run release:check (24 passing tests, typecheck, build, smoke, package smoke, release contract); bash scripts/validate.sh; git diff --check. Final diff, mergeability, branch protection, authorship, and head SHA were re-read.

Rebased/CI-repaired: no.

Verified head SHA: 51a6324.