feat: add upward config discovery and enhanced error messages

[davidturnbull]

Problem

Users must run CLI commands from the exact directory containing i18n.json, which creates a poor user experience:

• Running lingo.dev run from a subdirectory fails with a generic error
• Error message doesn't help users find their config file
• Common workflow of working in subdirectories (like src/, components/, etc.) is broken
• Inconsistent with other CLI tools like Git, which work from any subdirectory

Before:

cd my-project/src/components
lingo.dev run

❌ Error: i18n.json not found. Please run 'lingo.dev init'
# No helpful context

Solution

Commands now automatically search parent directories for i18n.json (similar to how Git finds .git) and provide helpful guidance when the config isn't found.

After:

# Works from any subdirectory
cd my-project/src/components
lingo.dev run

✅ Successfully finds ../../../i18n.json and runs

# When config truly not found, shows helpful error
cd ~/empty-directory
lingo.dev run

❌ i18n.json not found in current directory or parent directories.

Found 2 config file(s) in subdirectories:
  - project1/i18n.json
  - project2/i18n.json

Please cd into one of these directories, or run 'lingo.dev init'

Key Improvements

1. Upward Config Discovery: Commands search parent directories until they find i18n.json or reach the filesystem root
2. Smart Path Resolution: All file paths (lockfile, cache, bucket patterns) resolve relative to the config location
3. Enhanced Error Messages: When config not found, CLI searches subdirectories and lists found configs
4. Monorepo Support: In nested configs, the nearest config wins (enables per-package configs)
5. Consistent Experience: All commands (run, status, i18n) behave identically

Testing Instructions

Test 1: Run from subdirectory

cd packages/cli/demo/json/en
node ../../bin/cli.mjs show config
# Should display config from parent directory

Test 2: Helpful error messages

mkdir /tmp/test-parent
mkdir /tmp/test-parent/proj1 /tmp/test-parent/proj2
# Copy demo configs into proj1/ and proj2/
cd /tmp/test-parent
node path/to/cli.mjs run
# Should list both configs found in subdirectories

Test 3: Monorepo scenario

# Create nested configs and verify nearest one wins
mkdir -p /tmp/monorepo/packages/web
echo '{"locale":{"targets":["es"]}}' > /tmp/monorepo/i18n.json
echo '{"locale":{"targets":["fr"]}}' > /tmp/monorepo/packages/web/i18n.json
cd /tmp/monorepo/packages/web
node path/to/cli.mjs show config
# Should show targets: ["fr"] (nearest config)

Test 4: All commands work consistently

cd demo/json/deep/nested/subdirectory
node ../../../bin/cli.mjs status  # ✅ Works
node ../../../bin/cli.mjs run     # ✅ Works
node ../../../bin/cli.mjs show config  # ✅ Works

Behavior Notes

• Backward Compatible: Commands still work when run from the config directory
• Git-like: Searches upward only (doesn't search sibling directories)
• Performance: Config path is cached after first discovery
• Truncation: Error messages show max 5 subdirectory configs, then "... and N more"

What's Changed

• 9 files modified
• Config discovery logic centralized in utils/config.ts
• All commands now use getConfigOrThrow() for consistent error handling
• Path resolution updated to use config root directory

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