v7.1.0

Added

• Feat: add /llm-externalizer:llm-externalizer-scan-and-fix-serially command

Composition command that reuses the scan phase from scan-and-fix and
the serial loop from fix-found-bugs:

scan (parallel per-file reports)
-> aggregate into one canonical bug list
-> serial llm-externalizer-serial-fixer-agent loop (1 bug / dispatch)

Use this instead of scan-and-fix when fixes mutate shared state
(imports, types, schemas, shared mocks) — running 15 parallel fixers
would race — or when bug order matters (an earlier fix may supersede
or unblock a later one).

The command body is deliberately terse: ~60 lines of delta-only prose
pointing back to the two existing commands rather than re-inlining
their orchestration. Every token loaded into the slash-command
context is a token the orchestrator pays for — the longer the
description, the higher the floor per invocation. Treating this
command as "scan-and-fix scan phase + fix-found-bugs serial phase,
with these four deltas" keeps the marginal cost low.

README updates:

• 6 slash commands -> 7, new command added to the top bullet
• Commands table row added, describing the serial/stateful trade-off
• Plugin structure tree includes the new commands/*.md entry