Confirm screen and project plans from one proposal table, accept stringified tool arguments

[devfive-relay-c70423]

• Coerce tool arguments sent as strings (e.g. "60000") to the schema's number/boolean/array/object instead of rejecting them.
• devup_screen_plan / devup_project_plan draft returns proposal + proposalMarkdown: every open decision with its recommended answer, so the user confirms once (in their own language) instead of answering decision by decision.
• confirm takes acceptRecommended: true; only changed rows go in answers.
• A confirm that puts two screens on one URL writes nothing and returns details.conflict and details.retryAnswers with a distinct URL.
• Tool description, ASK_INSTRUCTION and devup / devup-implementation-plan skills updated; manifest hashes refreshed; changepack added.

Tests: fmt, clippy clean; cargo test -p devup-mcp passes except two symlink tests that need symlink privilege on Windows (OS error 1314, pre-existing).

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