Migrate examples to selective persistence (lvt:"persist" tag)

[adnaan]

Context

The livetemplate library is replacing always-on state persistence with selective persistence via the lvt:"persist" struct tag. This is a breaking change that requires updates to examples.

Library PR: livetemplate/livetemplate (branch: selective-persist)

What changed in the library

• WithEphemeralState() — removed
• lvt:"transient" — removed
• New: fields tagged lvt:"persist" are serialized to SessionStore and survive page refresh
• Fields without the tag are ephemeral (zero value on reload, loaded by Mount())
• No persist tags = fully ephemeral (equivalent to old WithEphemeralState())

Tasks

Delete redundant examples

• Delete ephemeral-counter/ — redundant; no persist tags = ephemeral by default
• Delete ephemeral-todos/ — redundant; regular todos/ now demonstrates the pattern

Add lvt:"persist" tags to examples with UI state

• todos/ (state.go) — tag SearchQuery, SortBy, CurrentPage, PageSize with lvt:"persist"
• todos-progressive/ — tag ActiveFilter with lvt:"persist"
• chat/ — tag CurrentUser with lvt:"persist"

Update support files

• test-all.sh — remove ephemeral-counter and ephemeral-todos entries (lines 39-40)
• README.md — remove ephemeral-counter/ and ephemeral-todos/ rows; note which examples use lvt:"persist"
• go.mod / go.sum — update livetemplate dependency to the version with this change

Examples that need no changes (correctly ephemeral)

counter, flash-messages, live-preview, login, profile-progressive, progressive-enhancement, shared-notepad, todos-components, ws-disabled, avatar-upload