feat(issue): add edit command with update alias

[camwest]

Summary

Add an issue field-mutation command with LLM-friendly naming:

• Canonical: isq issue edit
• Alias: isq issue update

Supported fields:

• --title
• --body (including --body - to read stdin)
• --priority (0..4)

Why

Issue #158 asked for a way to update mutable issue fields after creation so agents can keep the issue description current instead of appending workaround comments.

This keeps command vocabulary aligned with common CLI conventions (edit) while preserving update as an alias for discoverability.

Implementation

• Added IssueCommands::Edit with alias update in CLI args and command routing.
• Added new write op handler: src/cli/issues/write_ops/edit.rs.
• Added UpdateIssueRequest and Forge::update_issue trait method.
• Implemented per forge:
  • GitHub: updates title/body, rejects priority with explicit guidance.
  • Linear: updates title/body/priority via issueUpdate mutation.
  • JIRA: updates summary/description/priority (rejects --priority 4 since JIRA has no explicit "none" priority).
• Added offline queue support for edit operations in daemon processing.
• Added tests for:
  • CLI parsing (edit + update alias)
  • Edit command validation helpers
  • Linear priority mapping roundtrip
  • Conflict classification for Linear update mutation failures

Validation

• cargo test (197 passed)
• bash scripts/lint.sh --ci (clippy + fmt + file size checks all passed)

Closes #158

[camwest]

• feat(issue): add edit command with update alias #161 👈 (View in Graphite)
• master

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