refactor: remove hashline_read and hashline_edit tools #360

Hashline tools are experimental (OPENCODE_EXPERIMENTAL_HASHLINE flag, off by default), referenced by zero agent prompts, and actively causing pipeline failures. The regular read + edit/multiedit + write tools cover all capabilities.

Files to delete

• src/tool/hashline.ts
• src/tool/hashline_edit.ts + hashline_edit.txt
• src/tool/hashline_read.ts + hashline_read.txt
• test/tool/hashline.test.ts + hashline_edit.test.ts + hashline_read.test.ts (if exists)

Files to modify

• src/tool/registry.ts — remove flag check, always register edit tool, remove hashline registrations
• src/file/time.ts — remove hashlineRead state, hashlineRead(), assertHashlineRead()
• src/flag/flag.ts — remove OPENCODE_EXPERIMENTAL_HASHLINE
• .fork-features/manifest.json — record deleted files per fork governance

Acceptance Criteria

• All hashline source + test files deleted
• registry.ts: edit tool always registered, no flag suppression
• time.ts: hashlineRead state/functions removed
• flag.ts: OPENCODE_EXPERIMENTAL_HASHLINE removed
• .fork-features/manifest.json updated
• No references to hashline remain in src/
• bun run typecheck passes (0 errors)
• bun test passes (0 failures)