fix: annotate-last fails on Windows with non-ASCII paths

[backnotprop]

Summary

• Aligns projectSlugFromCwd regex with Claude Code's actual normalization: [^a-zA-Z0-9-] → - (was only replacing /)
• Adds case-insensitive fallback for directory lookup to handle Windows drive letter casing (C: vs c:)
• Adds tests for Windows backslashes, Cyrillic characters, underscores, spaces

Closes #339

Test plan

• Pull on Windows machine with non-ASCII project path (e.g. Cyrillic) and run /plannotator-last
• Verify session logs are found and last message renders in annotation UI
• Test with underscore-containing paths
• bun test apps/hook/server/session-log.test.ts passes (32/32)

[backnotprop]

Testing on Windows

Build from source (this PR)

# 1. Clone and checkout the branch
git clone https://github.com/backnotprop/plannotator.git
cd plannotator
git checkout fix/last-windows

# 2. Install deps and build the HTML assets
bun install
bun run build:hook

# 3. Compile the binary
bun build apps/hook/server/index.ts --compile --outfile plannotator.exe

# 4. Put it on PATH (or note the full path for step 5)
move plannotator.exe %USERPROFILE%\.local\bin\plannotator.exe

Use the local build instead of the marketplace install

Option A — --plugin-dir (uses the repo directly, no compile needed):

claude --plugin-dir ./apps/hook

Option B — Replace the compiled binary the marketplace plugin points to:

# Find where the current binary lives
where plannotator

# Replace it with the one you just built
copy /Y plannotator.exe <path-from-above>

What to test

1. Open Claude Code in a project with non-ASCII path (e.g. C:\Users\alexey\Documents\1С_конфигурации\ERP_Medicine)
2. Have at least one assistant response in the session
3. Run /plannotator-last
4. Verify the annotation UI opens with the last message
5. Also test with underscore paths (e.g. my_project) and paths with spaces