feat(server): redesign demo UI with real-time lattice and zoom (#387)

* feat(server): redesign demo UI with real-time lattice and zoom

- Add /lattice endpoint returning SVG as JSON
- Show morpheme table and lattice graph side-by-side in real time
  (previously lattice opened in a new tab via Lattice button)
- Highlight lattice node on morpheme row click
- Add zoom controls (＋/－, Fit, Reset, Ctrl+wheel) for SVG graph
- Auto-fit zoom to container on each analysis
- Split inline CSS/JS into asset/demo.css and asset/demo.js
- Embed assets via embed.FS; serve static files at /asset/

* chore: fix golangci-lint errors in LatticeHandler

* chore: fix demo HTML bugs and add LatticeHandler tests

* refactor(server): hide HTML templates from /asset/ and clean up

* chore(server): skip lattice rendering on empty input

* feat(server): add SVG/PNG download dropdown to lattice demo UI

* feat(server): improve lattice zoom anchoring and morpheme selection

* docs: replace webapp gif with demo video in README

Merge pull request #378 from ikawaha/bump_20260103

chore: Bump kagome-dict from v1.1.6 to v1.1.7

chore: Update kagome-dict and fix Go version (#356)

* chore: Update kagome-dict

* chore: Replace b.Loop() with for loop for Go 1.23 support

* chore: Replace t.Context() with context.Background() for Go 1.23 support

Merge pull request #344 from ikawaha/bump/kagome-dict-v1.1.2

chore: Bump kagome-dict from v1.1.0 to v1.1.1 (ipa/v1.2.1, uni/v1.2.1)

Merge pull request #340 from ikawaha/develop

Release candidate

chore: Update

Merge pull request #338 from KEINOS/fix-337-update-goreleaser-conf-v0…

…-to-v2

fix: goreleaser conf v0 --> v2 (#337)

Merge pull request #336 from ikawaha/develop

Release candidate

Merge pull request #330 from ikawaha/develop

Release candidate

Merge pull request #325 from ikawaha/develop

Release candidate