Unify text input handling and bump WASM ABI to 0.25.0

[Yus314]

WASM ABI 0.25.0: unify text input handling, fix GUI IME, and rename clipboard paste command

Summary

This PR does two related pieces of work:

1. Rebuilds input handling around a shared TextInput semantic path.
2. Bumps the WASM plugin ABI to kasane:plugin@0.25.0 and renames clipboard paste from Paste to PasteClipboard.

The immediate user-visible result is that GUI IME now works correctly, text-producing inputs are routed consistently, and clipboard paste is clearly separated from committed text input.

Problem

Before this change:

• GUI IME enabled only partial support.
• Preedit was discarded, so composing text was not visible.
• Candidate window positioning was not synchronized to the rendered caret.
• IME commit was treated as key input instead of text input.
• Plain char input, IME commit, bracketed paste, and clipboard paste used different paths.
• The plugin ABI still used Paste, even though its meaning had narrowed to host clipboard insertion.

Design

The main design decisions are:

• Treat Preedit as GUI-local runtime state, not editor truth.
• Treat committed text as TextInput(String), not KeyEvent.
• Keep IME candidate positioning tied to rendered caret coordinates, not raw model cursor state.
• Route focused surface input before editor/plugin fallback.
• Unify text-producing inputs onto one semantic text pipeline.
• Reserve a separate command only for host system clipboard insertion.
• Make the clipboard rename explicit in WIT via an ABI bump.

Scope

This PR includes:

• GUI IME state and rendering.
• Core TextInput semantics.
• Plugin and surface text-input routing.
• Clipboard paste semantic cleanup.
• WASM ABI bump to 0.25.0.
• SDK/docs/manifests/artifacts updates.

Key Changes

IME / GUI

• Added GUI-local IME state in kasane-gui.
• Moved WindowEvent::Ime handling out of generic input conversion.
• Rendered Preedit as an overlay.
• Synced candidate window position via set_ime_cursor_area(...).
• Added target binding so stale preedit is cleared when session/target changes.
• Improved preedit rendering using cursor_range for active segment/caret display.

Core Input Model

• Added InputEvent::TextInput(String).
• Added core text-target resolution.
• Normalized plain text chars into TextInput when a text target is active.
• Routed IME commit, bracketed paste payloads, and plain text through the same semantic path.

Commands / Event Loop

• Added Command::InsertText(String) as the semantic command.
• Compiled InsertText to Kakoune Keys(...) only at the host boundary.
• Added common event-loop dispatch so injected input, clipboard paste, and normal input share the same routing stages.

Plugin / Surface Routing

• Added plugin observe/handle hooks for committed text input.
• Added focused-surface text-input consume path.
• Added focused-surface key consume path so surface routing is consistently surface-first.

Clipboard Paste / ABI

• Renamed WIT command paste to paste-clipboard.
• Renamed session-ready variant accordingly.
• Bumped package ABI to kasane:plugin@0.25.0.
• Updated host conversion, SDK helpers, manifests, fixtures, bundled plugins, and docs.

Important Behavioral Changes

• GUI IME preedit is visible.
• Candidate window follows the rendered caret.
• IME commit no longer goes through key semantics.
• Plain character input in active text targets now uses the text pipeline.
• Bracketed paste payloads now preserve and route actual text.
• Clipboard paste remains explicit and separate via PasteClipboard.
• Focused surfaces can consume both key input and text input before editor/plugin fallback.

Migration

For plugin authors upgrading from ABI 0.24.0:

• Update abi_version = "0.25.0" in kasane-plugin.toml.
• Update SDK to kasane-plugin-sdk = "0.4".
• Rename Command::Paste to Command::PasteClipboard.
• Prefer the helper paste_clipboard().
• Rebuild and reinstall the .wasm.

Committed text input and bracketed paste payloads do not use PasteClipboard.

Notable Fix During Rollout

While validating the ABI bump, bundled pane_manager.wasm was still exporting kasane:plugin/plugin-api@0.24.0. That stale artifact caused bundled discovery failures and extra diagnostics. This PR replaces it with the rebuilt 0.25.0 artifact and adds a regression test for manifest-path loading.

Tests Run

• cargo test -p kasane-gui --lib
• cargo test -p kasane-tui --lib
• cargo test -p kasane-core state::tests::update -- --nocapture
• cargo test -p kasane-core state::tests::input -- --nocapture
• cargo test -p kasane-core event_loop::tests::surface -- --nocapture
• cargo test -p kasane-core event_loop::tests::dispatch -- --nocapture
• cargo test --manifest-path kasane-plugin-sdk/Cargo.toml -- --nocapture
• cargo test -p kasane-wasm --lib -- --nocapture

Review Guide

Suggested review order:

1. kasane-gui
2. kasane-core/src/input
3. kasane-core/src/state/update.rs
4. kasane-core/src/plugin/*
5. kasane-core/src/surface/*
6. kasane-core/src/event_loop/*
7. kasane-wasm/wit/plugin.wit
8. kasane-wasm/src/convert/*
9. SDK/docs/manifests/artifacts

Focus questions:

• Is Preedit ownership correctly isolated to the GUI layer?
• Is TextInput now the right semantic boundary for committed text?
• Is the surface-first routing order correct?
• Is PasteClipboard now semantically narrow and well-separated?
• Does the ABI bump cover all host/SDK/artifact boundaries?

Risk Areas

• Buffer text-target detection still uses heuristic information in some cases.
• Unicode grapheme fidelity is improved but not fully reworked.
• This is a real ABI break for WASM plugins and requires rebuilds.

Docs Updated

• README.md
• docs/plugin-development.md
• docs/using-plugins.md
• kasane-plugin-sdk/README.md