docs: four sites credit SQLBaseProvider with placeholder generation it does not have

[cevheri]

#640 counted five sites and I wrote the grep that counted them. It looked for the literal getPlaceholder, so it missed every site that paraphrases the name instead of writing it. #642 fixed the five and left four behind.

SQLBaseProvider has no placeholder logic of any kind. Measured on main at db40452, src/lib/db/providers/sql/sql-base.ts declares eight members and not one of them mentions a placeholder:

escapeIdentifier  buildLimitClause  shouldEnableSSL  getInformationSchemaName
getDefaultSchema  isReadOnlyQuery   isSchemaModifyingQuery  prepareQuery

The real home is positionalPlaceholder() in src/lib/sql/values.ts:148, a module-level function that no provider calls at all. Its only caller is src/hooks/use-inline-editing.ts:107.

The four sites

Site	What it claims
docs/ADDING_A_PROVIDER.md:37	lists "placeholder style" among what SQLBaseProvider gives a new SQL provider
docs/DATABASE_PROVIDERS.md:108	"SQLBaseProvider provides SQL-specific helpers (LIMIT injection, identifier escaping, placeholder generation)"
docs/DATABASE_PROVIDERS.md:119	"identifier escaping and the placeholder style are inherited rather than rewritten"
docs/providers/postgres.md:42	"the shared SQL mechanics (identifier quoting, LIMIT injection, dialect placeholders, SSL auto-detection) live in SQLBaseProvider"

Two of these files already carry the correct version of the same fact, a couple of hundred lines away, so each one currently asserts both things:

• docs/ADDING_A_PROVIDER.md:262 says positionalPlaceholder() is in values.ts and "not inherited" - while sitting under the heading What SQLBaseProvider adds.
• docs/providers/postgres.md:83 says "shared rather than inherited".

The rule for the fix

Same one you applied in #642: keep the fact, drop the wrong attribution.

DATABASE_PROVIDERS.md:119 is the one to be careful with. It is a compound claim and only half of it is wrong: escapeIdentifier() really is inherited by ClickHouseProvider, DruidProvider and TrinoProvider (none of the three overrides it, ClickHouse only calls it), and double-quoted identifiers really are correct in all three dialects. Split the sentence rather than deleting it.

The wording docs/providers/clickhouse.md:126 and docs/providers/druid.md:131 now carry, after your PR, is the model:

Not in the list: a placeholder helper. SQLBaseProvider no longer has one (#304 removed it).

Two smaller things in the same sentence at docs/ADDING_A_PROVIDER.md:35-37, worth doing in the same edit:

• It calls sql-base.ts "[153 lines]". The file is 159. It was 153 when docs: split provider reference from the add-a-provider guide #266 wrote that, then 165, then 178, and 159 since 02578ff7 - which is fix(sql): bind the inline row edit's values, and quote the remaining interpolated ones (#290) #304, the same commit that deleted getPlaceholder(). A hardcoded line count in prose cannot be cited by name and no test can hold it, so drop the count and keep the link.
• The positionalPlaceholder() row belongs under a heading other than What SQLBaseProvider adds, or that heading needs to stop covering it.

The guard

This is the part that matters, and it is why this is a separate issue rather than a second commit on #642. Nothing in the suite mentions placeholders, so all nine sites went stale in silence and the four left could come back the same way. Add both of these to tests/unit/provider-docs-monitoring-citations.test.ts:

1. Extend the existing list. docs/DATABASE_PROVIDERS.md is not in TOP_LEVEL_NAMED_CITATION_DOCS (line 382). It carries zero .ts:<line> citations today, so adding it costs nothing and locks in what is already true.

2. A new test for the attribution. Assert that no line in these docs names SQLBaseProvider, or claims inheritance, together with a placeholder phrase.

Two traps to design around, both of which have bitten this file before:

• Do not assert on the word. "docs/ADDING_A_PROVIDER.md must not contain placeholder" is a false-red machine: line 262 legitimately names positionalPlaceholder(), line 619 documents a searchPlaceholder label, and postgres.md:83 and :705 are both correct as written. Assert on the attribution, not the token.
• Pair the negative with a control. A test that only asserts absence passes just as well when the docs are empty. Add a positive assertion of the fact it depends on: positionalPlaceholder is declared in src/lib/sql/values.ts, and sql-base.ts declares no member matching /placeholder/i. If someone later moves that logic into the base class, the control goes red and the guard has to be rewritten on purpose instead of quietly meaning nothing.

Verifying

• grep -rniE 'placeholder' docs/ | grep -iE 'sqlbaseprovider|inherit' should return only sentences that are true.
• bun run test stays green. postgres.md is in this file's NAMED_CITATIONS and ADDING_A_PROVIDER.md is in TOP_LEVEL_NAMED_CITATION_DOCS, so both are already in scope for the no-line-number tests.
• The new test must fail on today's main. Write it first, watch it name the four sites, then fix them. A guard that was never seen red is not a guard.
• 100% line coverage is a hard gate, but a test-only change adds no executable lines to src/.

@XiaoZ-0218 said on #642 they would take this. It is theirs.

[XiaoZ-0218]

Taking this.