Add --resolve and --resolve-file flags to plan update

Extend the refrakt plan update command to accept resolution content and append a ## Resolution section to work item and bug files.

Acceptance Criteria

--resolve <text> flag appends a ## Resolution section before the closing rune tag
--resolve-file <path> reads resolution body from a file
Completed: <today's ISO date> is auto-prepended as the first line of the section
Resolution section is inserted before {% /work %} or {% /bug %} closing tag
If a ## Resolution section already exists, new content is appended with a --- separator
--resolve can be combined with --status done in a single command
--resolve can be used standalone (without changing status) for incremental updates
--resolve is only allowed on work and bug rune types (error for spec/decision/milestone)
Unit tests cover: new resolution, append to existing, combined with status change, standalone resolve, file input, type restriction

Approach

Extend UpdateOptions in runes/plan/src/commands/update.ts with resolve?: string and resolveFile?: string. After applying attribute and checkbox changes, if resolve content is provided, locate the closing rune tag and insert the formatted Resolution section. Parse --resolve and --resolve-file in the CLI plugin's argument handling.

References

SPEC-027
WORK-071 — scanner must understand resolution format (parallel, not blocking)