pi-image-paths: attach dropped image paths and draw them in the chat

A screenshot is normally sent to pi as a path, so the model gets its text and
the reader gets nothing: pi renders image blocks in tool results but never on
user messages. This extension closes both halves — the path collapses to
"[Image #N]" as you type or on send, and the picture is drawn below the sent
message.

The rewrite is a terminal-input listener that re-reads a settled editor, joins
word by word for paths with unescaped spaces, and reports a path that does not
exist instead of eating the prompt. The drawing appends a custom session entry
carrying the message's image blocks, one macrotask after message_end so it lands
below the message pi persists afterwards, and renders it with pi-tui's inline
image component under terminal.showImages and terminal.imageWidthCells. Entries
stay out of the model context, so each image is still sent to the model once.

Tests: npm test (21, node:test over a stand-in for pi: rewrite, send-time
attachment, missing paths, append gate, renderer gating) and npm run typecheck.

Co-Authored-By: nw-flash-flex <noreply@freno.me>

LICENSE

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+MIT License
+
+Copyright (c) 2026 Michael Freno
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.