fix: drop stale canvas element when ids collide with a different tag

[avanelsas]

Summary

Loading a project file while another doc was open could leave
visible residue from the previous document — kinetic-typography
animations, particle-button effects, gaussian-blur layers, etc. —
inside what should be a fresh tree.

Repro: open the Kinetic Showcase template, then File → Open
another project. Effects from the kinetic template bleed into the
new view.

Root cause

Every Bareforge document starts its `:next-id` counter at 0,
so two unrelated documents share the same id space (`n_0`,
`n_1`, …). When `apply-loaded-project!` swaps `:document`,
`patch!` walks the new doc and `upsert-node!` finds an
existing element in `node-index` for each colliding id. The
fast path just diffs attrs / props / text — it never checked
whether the existing element's TAG matches the new node's tag.

If kinetic's `n_5` was an `x-particle-button` and the new
doc's `n_5` is a plain `x-button`, the existing custom element
keeps its tag (and all the side-effect state attached to it:
animation loops, canvas pixels, internal listeners, portaled
scrims). Only its attrs get diffed.

Fix

`upsert-node!` now checks `(.-localName prior)` against the
new node's `:tag`. On mismatch it calls `rec/remove-el!`,
deletes the index entry, and falls through to the create path so
a fresh custom element takes over. The full subtree rebuilds
because the children's parent pointer changes.

Test plan

• cljfmt check — clean
• npx shadow-cljs compile test — 584 tests, 0 failures
• npx shadow-cljs release app — 0 warnings under Closure Advanced
• clj-kondo — 0 errors, 0 warnings
• Manual repro:
  • Open Kinetic Showcase template.
  • File → Open one of the `demo-store-*.json` fixtures.
  • Verify no kinetic typography / particle effects / blur layers persist in the new view.

The shared-id-different-tag scenario has no node-test coverage
because canvas-reconciler tests need a real DOM (browser-test build)
and the project hasn't wired up that test target yet. Manual repro

• the existing 584-test gate are the verification.

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