Remove code that nothing calls or reads

[zibo-yang]

Fixes #113.

What changes

Deletions only (58 lines, nothing added):

• autoform_cli/render.py: _inject_after_title, _status_phrase, _markdown_table_cell and _shift_headings. The first and last were near-copies of the live _inject_after_lead and _demote_headings.
• autoform_cli/claims.py: ClaimBoard.gc, an alias for cleanup().
• servers/repl/core.py: the LeanReplConfig.mem_interval_check field.
• servers/repl/pool.py: the constant DEFAULT_PORT.
• render.py tidying: an empty f"" fragment in the progress overview and nine surplus blank lines. Two of those blank lines (before _next_target and before STRUCTURE_PAGE) are not listed in Remove dead code in render.py, claims.py and the REPL server #113; they were the same kind of leftover.

ClaimBoard.holds, ClaimBoard.heartbeat and Heartbeat are untouched, as the issue asks.

How it was checked

• None of the seven symbols is referenced anywhere in the tree after the change, or on the execution branch. Every LeanReplConfig(...) construction uses keyword arguments and none passes mem_interval_check.
• vulture autoform_cli servers reported exactly these seven before the change and none of them after.
• make lint passes and make test gives 1026 passed, 34 skipped.
• Rendering the example blueprint from clean checkouts of the base and of the original removal gives the same 24 files apart from the embedded commit SHA; audit and check output are identical. This comparison was not repeated after the two extra blank lines were removed.
• make check-example and the strict MkDocs build were not run.

Notes for reviewers

• Replace custom Lean servers with managed Lean Beam #76 also deletes mem_interval_check and DEFAULT_PORT, so whichever of the two lands second will have a trivial conflict in servers/repl.
• The stale branch vivc/dev still calls the four render helpers in its own older render.py. It is not an open pull request, but it would need them ported if it is ever rebased.
• Remove dead code in render.py, claims.py and the REPL server #113 says autoform_worker/cli.py does not exist on execution. It does exist there, but it calls cleanup() and not gc, so the conclusion holds.

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