chore(context7): drop the stale planning/ exclusion

[lesnik512]

context7.json excludes a planning/ directory that no longer exists. This repo migrated off the planning/ convention, and the exclusion has been a dead entry since — it was left behind because it sat outside that migration's recipe, so removing it is an independent call rather than migration fallout. Part of the cleanup around modern-python/.github#67.

Why drop the key rather than leave an empty list

Checked against Context7's published schema (https://context7.com/schema/context7.json) rather than assumed:

• the schema declares no root required array, so every property is optional;
• excludeFolders carries "default": [] and no minItems.

An absent key and [] are therefore equivalent to Context7. Absent is what the repos that never carried the line already look like (eof-fixer, faststream-concurrent-aiokafka), so dropping it converges the org on one shape.

Non-goals

No other exclusion is touched — this repo excluded only planning, so there is no partial-list edit. Indexing behaviour is unchanged, since the excluded path does not exist.

Verification

• git ls-tree -d origin/main planning returns nothing: the directory is genuinely absent at main, not merely absent from the working tree.
• just lint-ci clean.

[github-actions]

Benchmark gate

✅ gate passed

scenario	msg/s	delete/msg	WALrec/msg	WALB/msg	fpi	upd	del	dead_tup
consumer/w1/b10	1034	1.000	6.79	916	242	5000	5000	10000
consumer/w1/b100	1041	1.000	6.82	920	243	5000	5000	10000
consumer/w2/b10	1208	1.000	6.79	962	242	5000	5000	10000
consumer/w2/b100	1418	1.000	6.73	956	243	5000	5000	10000
consumer/w4/b10	1075	1.000	6.82	995	261	5000	5000	10000
consumer/w4/b100	1641	1.000	6.87	1040	244	5000	5000	10000
consumer/w1/b100/tfbs100	6793	0.010	6.07	1116	243	5000	5000	10000
producer/w1/b100	2328	0.000	3.04	584	0	0	0	0

Gated (fails the build): delete_calls + tuple counters (upd/del/ins) + the producer's insert_calls, exact; select_calls within +2; wal_records within a 10% band. msg/s, WAL bytes and total calls are informational (timing/FPI noise).