Consider enabling lychee text-fragment checking (include_fragments = "full")

lychee 0.24.x (arriving via lychee-action v2.9.0, PR #324) replaced the boolean `include_fragments` with a `FragmentMode` enum: `none` / `anchor-only` / `text-only` / `full`. #324 sets `anchor-only` to preserve the prior behavior exactly and keep the version bump behavior-neutral.

`full` additionally checks text fragments (`#:~:text=...`), which is new in 0.24.x. Enabling it is a deliberate behavior change, not a version-bump side effect, so it lives here as its own decision.

Before flipping to `full`:

- Confirm whether any posts use text-fragment links today (`grep -rn "#:~:text=" src/data/blog/`), since those would newly be validated.
- Weigh flakiness: text-fragment matching depends on the target page's current text, which drifts more than anchors.

If there's no current usage and low appetite for the extra flake surface, closing not-planned is a fine outcome.