feat: web clipper browser extension

[tstapler]

Problem

SteleKit has no one-click way to capture a web page (or a screenshot/selection) directly into the graph from the browser. Trilium Notes ships a web clipper extension for exactly this (https://docs.triliumnotes.org/user-guide/setup/web-clipper).

stelekit-import (see project_plans/stelekit-import/requirements.md) covers pasting raw text or a URL inside the app and auto-linking it to existing pages — that's a different entry point than "I'm reading something in my browser right now and want to save it with one click," which requires no context switch back to SteleKit.

Why this matters

• Reduces the "I found something interesting" → "it's in my graph" friction to near-zero for the single most common capture trigger: browsing.
• Complements, rather than duplicates, stelekit-import's topic-suggestion logic — the clipper can hand off captured content to that same auto-linking pipeline once it lands in the graph.

Suggested scope (v1)

• Browser extension (Chrome/Firefox via WebExtensions API) with a toolbar action: clip current page (readability-extracted article content) or a screenshot.
• Requires SteleKit to expose some local write path for the extension to talk to — likely the same local API surface proposed in the automation-API issue in this repo, rather than inventing a second one.
• Out of scope for v1: full-page archival/snapshotting (vs. article-content extraction), Safari support.

References

• Related: project_plans/stelekit-import/requirements.md (in-app paste/URL import — different trigger point)
• Depends on a local API surface — see the automation-API issue filed alongside this one