[tooling]: scoped lpd mint dev profiles to fix startup and route latency

[DeveloperAlly]

Problem

Local lpd dev / lpd mint dev startup is frequently 5+ minutes and route transitions are extremely slow or crash-prone in this repository's large multilingual docs config.

Impact

• Blocks iteration velocity for docs maintainers.
• Makes Mint preview unreliable for routine edits.
• Increases local failure rates due to stale concurrent Mint processes.

Requested Change

Implement scoped dev profiles for lpd mint dev so maintainers can run a reduced local docs surface (e.g. v2+en, selected tabs/path prefixes) without mutating production docs.json / .mintignore.

Scope In

• lpd
• tools/scripts/mint-dev.sh
• tools/scripts/dev/generate-mint-dev-scope.js
• tests/unit/lpd-scoped-mint-dev.test.js
• docs-guide/lpd.mdx
• README.md

Scope Out

• v1/
• Production deploy behavior for full docs config
• Unrelated workflows/scripts

Acceptance Checks

• node tests/unit/lpd-scoped-mint-dev.test.js
• node tests/unit/script-docs.test.js --files tools/scripts/dev/generate-mint-dev-scope.js --enforce-existing
• node tools/scripts/validate-codex-task-contract.js --branch codex/<issue-id>-scoped-lpd-mint-dev-profiles --validate-contract-only
• node tests/run-pr-checks.js --base-ref docs-v2

Risk Flags

• generated-files
• ci-impact