fix: order issue-type keyword rules by signal strength #3577

Found by Qodo review of #3573 (merged as #3568's fix).

Problem

derive-project-fields.cjs orders TYPE_KEYWORDS most-specific-last in practice: type:feature sits second and its patterns include bare action verbs (add, implement, build, develop) that appear in almost any title. inferMappedValueFromText takes the first rule that both matches and has a configured mapping, so the generic rule shadows every subject rule below it.

Verified as pre-existing: the same titles resolved to Feature before #3568, so this is a latent weakness rather than a regression from that fix.

Approach

Ordered cascade, most-specific signal first, first match wins — the pattern OpenAlex used when reclassifying 49.6M works ("Rules are ordered by measured trustworthiness: unambiguous structural signals fire first, softer text heuristics later").

Move only the generic type:feature rule to the end of the array and leave every other rule's relative order untouched, so the change is limited to the reported problem. Keep type:test above type:compat so integration test stays a test.

Acceptance

• A title naming a subject classifies by that subject even when it starts with a verb
• type:feature still classifies genuinely feature-shaped titles
• An explicit type:* label still beats every keyword rule
• No change to project_field_mappings.Type, .github/issue-types.yml or any locked file
• Regression tests pin the ordering so a later rule insertion cannot reintroduce the shadowing