feat: add jsx-no-conflicting-pragmas rule

[bartlomieju]

Adds a rule that flags mixing the automatic-runtime pragma
@jsxImportSource with the classic-runtime pragmas @jsx /
@jsxFragment (or @jsxFrag) in the same file:

/** @jsxImportSource https://esm.sh/preact */
/** @jsx h */
/** @jsxFragment Fragment */

When @jsxImportSource is set the file uses the automatic runtime, so the
@jsx and @jsxFragment pragmas are silently ignored. Having both is a
footgun — you should use one runtime or the other. The rule reports each
classic pragma when an @jsxImportSource pragma is also present, and only
looks at the file's leading comments, where pragmas actually take effect.

The rule is tagged react/jsx but intentionally left out of
recommended, so it must be enabled explicitly. Happy to promote it to
recommended if preferred — flagging the decision rather than making it.

Closes #969.

[bartlomieju]

Verdict: LGTM — correct and well-tested. Recommend merge after resolving the schema conflict + rebase (new rule → maintainer product decision, which you've explicitly flagged). Not auto-merging (new rule).

Correctness — verified the regex boundaries (the crux of this rule)
I simulated both patterns against the tricky inputs; all behave exactly as documented:

• @jsxImportSource\b matches @jsxImportSource but not @jsxImportSourceTypes (the T after Source blocks the \b) — so a types-only directive doesn't switch the runtime. ✓
• @jsx(Frag(ment)?)?\b matches @jsx, @jsxFrag, @jsxFragment, but not @jsxImportSource, @jsxRuntime, or @jsxFragmentFoo (word-boundary correctly rejects longer identifiers). ✓
• Logic is order-independent and only inspects comments before the first statement (where pragmas actually take effect); comment-only files fall back to scanning all comments. All of this is covered by the valid/invalid tests, including the multi-pragma and reversed-order cases.

Perf: fine — two Lazy-compiled regex is_match calls per leading comment; leading comments are few.

Minor

• A single comment holding both @jsxImportSource and a classic pragma gets flagged as a whole (range = full comment). Reasonable; just noting the range granularity.
• No docs/rules/jsx_no_conflicting_pragmas.md / docs() in the diff — new rules conventionally ship docs, and the docs.json CI diff expects them.

Housekeeping / blockers

• Edits schemas/rules.v1.json, which PR chore: remove schema files for rules and tags #1377 deletes — these will conflict; coordinate ordering and drop the schema edit if chore: remove schema files for rules and tags #1377 lands first.
• mergeable: UNKNOWN → rebase.
• The recommended promotion is yours to call — you've flagged it; opt-in is a fine default.

No code changes requested. Solid rule; just docs + the schema-file conflict + rebase before landing.