Separate line protocol syntax reference from write-execution semantics

_Describe your proposal here._

`content/shared/v3-line-protocol.md` is titled and scoped as a **syntax** reference: table, tag set, field set, timestamp, data types. #7682 and #7692 added **write-execution semantics** to the same page: duplicate-point overwrite resolution, compactor/snapshot timing, multi-ingest-node routing, and product-specific delay recommendations. That content depends on the storage engine, not the protocol — a valid line protocol point is the same string regardless of when or whether an overwrite resolves deterministically.

Putting execution semantics into the syntax reference forced three-way `show-in`/`hide-in` branching (distributed vs. Enterprise vs. Core, plus a fourth Cloud case) to compensate for what's really a per-product routing problem, not a syntax difference. Follow-on fixes in #7692 (cross-links, cloud scope, wording) had to patch each branch separately, and the same maintenance cost will recur on the next storage-engine change.

##### Proposal

Move overwrite-timing/duplicate-point-resolution content out of the line protocol syntax reference and into a write-data or data-model doc per product (or a shared `write-data` doc, if the same `show-in` pattern still applies there — TBD). Leave a single short pointer from the syntax reference to that doc.

Expected effect: most of the `show-in` branching in the "Duplicate points" section collapses, because the product-specific mechanics live where they're inherently product-specific (write/storage docs), instead of being spliced into shared syntax content that's otherwise product-agnostic.

##### Non-goals

- Not proposing to change the technical content itself (already reviewed in #7682/#7692), only where it lives.
- Not proposing to touch the distributed products' existing "Performance considerations" / "Retention guidance" sections beyond relocating what already moved in #7692, unless the same split makes sense there too.

##### Relevant URLs

- https://github.com/influxdata/docs-v2/pull/7682
- https://github.com/influxdata/docs-v2/pull/7692
- content/shared/v3-line-protocol.md (Duplicate points section)

Start with content/shared/v3-line-protocol.md and its Duplicate points section, then review the changes and scope in #7682 and #7692. Determine whether the execution semantics belong in product-specific write-data or a shared write-data document. Done means the syntax reference keeps only a short pointer, with execution guidance relocated and unnecessary show-in branching removed.

Written by the indexing model from the issue text.