fix(editor): allow hyperlink clicks in locked edgeless text blocks (#14829)

Fixes #14673

## Summary

When an edgeless text block is locked, `pointer-events: none` on the
inner content div (`edgeless-text-block.ts:308`) blocks all mouse
interaction — including clicking hyperlinks. Locking is intended to
prevent accidental edits, not to block navigation, so links should
remain clickable.

## Fix

Apply a `locked-content` class on the inner div when the block is locked
and not being edited, and add a targeted CSS rule restoring
`pointer-events: auto` on anchor elements within locked content.

## Context

Re-implements the fix from PR #14692 (authored by @moktamd, reverted per
@darkskygit's comment on #14673 because the original contributor had not
signed the CLA). The CLA is signed for this PR.

## Test plan

- [ ] On edgeless canvas, create a text block with a hyperlink (e.g.
`[link](https://affine.pro)`)
- [ ] Lock the block via the shape toolbar
- [ ] Hover the link → cursor shows pointer
- [ ] Click the link → navigation occurs
- [ ] Unlock and confirm editing still works as before

<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit

* **Bug Fixes**
* Links within locked text blocks are now interactive and clickable with
proper visual cursor feedback.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->