docs: correct data workflows, SQL and operations (#4534)

This PR is part of the documentation revamp. Once the full set of PRs is
merged, we’ll publish the combined site to staging for review before
updating docs.lancedb.com.

The curation, SQL and operations pages contain outdated claims and
examples that do not reliably work as written.

This corrects those pages against the reviewed SDK and local server
evidence, including prepared statements, background jobs, cleanup and
monitoring. Integration guides are grouped with their examples in #4533.

Function and Secret-object documentation stays unpublished until its
release. The two Function pages are listed in `.mintignore` and left out
of the navigation, and the sections about them on other pages are MDX
comments.

Stacked on #4533. Each MDX file has one PR owner. Rebase onto main after
#4533 is squash-merged.

Local assembly, Mint validation and link checks pass, and the assembled
site shows no Function or Secret-object content. A local release
rehearsal that uncomments the drafts and restores the navigation also
passes. Hold publication until this PR and lancedb/sophon#8688 are on
`main`.

docs/web/sql/dql/sampling.mdx

@@ -6,12 +6,11 @@ icon: dice
 keywords: ["tablesample", "sampling", "bernoulli", "system", "repeatable", "random"]
 ---
 
-<Badge color="red">Enterprise</Badge> [SQL runs on a deployment.](/sql)
+<Badge color="red">Enterprise</Badge> [SQL runs in LanceDB Enterprise.](/sql)
 
-`TABLESAMPLE` draws a random subset of a table. On a lakehouse table that is
-often the difference between a question you can afford to ask and one you
-cannot -- an aggregate over 1% of forty billion rows answers in a fraction of
-the time, and for most estimates that is enough.
+Use `TABLESAMPLE` to explore a subset of a table or estimate aggregate
+statistics. The sampling method determines how much data is read and whether
+the table's physical layout influences the sample.
 
 ```sql
 SELECT * FROM documents TABLESAMPLE (10)        -- 10 percent
@@ -41,8 +40,8 @@ only as uniform as the data's layout. If rows were written in an order that
 correlates with what you are measuring, a fragment sample inherits that
 correlation.
 
-Reach for `SYSTEM` when you want a cheap look at the data and `BERNOULLI` when
-the number you compute has to be defensible. Omitting the method gives
+Use `SYSTEM` for a quick look at the data and `BERNOULLI` when you need
+independent row sampling. Omitting the method gives
 `BERNOULLI`.
 
 ## Repeatability {#repeatable}
@@ -54,9 +53,10 @@ different rows. `REPEATABLE` fixes the draw:
 SELECT * FROM documents TABLESAMPLE (10) REPEATABLE (42)
 ```
 
-This is what makes a sample usable as a **fixed evaluation set**: the same seed
-against the same data gives the same rows, so a metric computed today is
-comparable with one computed last week.
+Use the same seed and table snapshot to reproduce a sampling run. For a fixed
+evaluation set, save the selected row IDs or materialize the sample and retain
+its version. A seed alone does not preserve membership after source changes
+or changes to the physical layout.
 
 ## Where the clause can go {#placement}
 
@@ -64,7 +64,7 @@ It attaches to a table in `FROM`, including inside a subquery, a CTE, or either
 side of a join:
 
 ```sql
-SELECT * FROM (SELECT * FROM documents) d TABLESAMPLE (10)
+SELECT * FROM (SELECT * FROM documents TABLESAMPLE (10)) d
 
 SELECT * FROM a TABLESAMPLE (5 ROWS) JOIN b ON a.id = b.id
 
@@ -75,7 +75,7 @@ Each side of a join samples independently. Sampling both sides of a join
 shrinks the *result* far more than either fraction suggests, because a row only
 survives if both its sides were drawn.
 
-## What is refused {#refused}
+## Unsupported sampling forms {#refused}
 
 Sampling is semantics, not a hint. A clause that were read and then not applied
 would be a wrong answer rather than a missing feature, so anything that cannot
@@ -86,6 +86,7 @@ be honoured exactly is an error:
 | `TABLESAMPLE (101)` | a percentage outside `0..=100` is refused, not clamped |
 | `TABLESAMPLE (1.5 ROWS)` | a row count must be whole |
 | `TABLESAMPLE (BUCKET 1 OUT OF 4)` | bucket sampling is not supported |
+| `(SELECT ...) d TABLESAMPLE (10)` | a subquery's result cannot be sampled; sample the table inside it |
 | the `SAMPLE` spelling | use `TABLESAMPLE` |
 | the `OFFSET` modifier | not supported |