feat(sources v1): the agent locates files itself — ls/find/grep + tool-call cards

User pivot (2026-09-19): no attachments UI at all. Pasting paths is native
for technical users and alien for everyone else - so the agent gets the
tools to find what the learner merely NAMES. The learner communicates in
messages; the agent locates and reads. Zero cross-stream seams: paths
already live in tool parts, so the sources "list" is the transcript.

- ls/find/grep: pi-verbatim schemas, descriptions, and output formats
  (fd's glob semantics, rg's path:line: match format, pi's truncation
  notices), ported to pure Node - no binaries, no shell-out, read-only by
  construction. Deltas from pi: home-anchored resolution (the harness has
  no cwd), .gitignore replaced by hard noise exclusions
  (node_modules/.git/Library/.Trash), 10s walk timeout with partial results.
- read: description swapped to pi-verbatim (doctrine moved to the prompt);
  relative paths now resolve against the learner's home like the rest.
- prompts/shared/05-learner-files.md: one minimal doctrine fragment
  composed into BOTH agents (composeInstructions grew a shared/ dir,
  before the agent's own fragments). teacher/30-jobs.md keeps only the
  pdf-dispatch addendum.
- ToolCallCard: the generic quiet tool-call card the user specced -
  collapsed one-liner (tool name + headline argument), expandable to full
  input/output, errors red, image payloads never render. Registered for
  read/ls/find/grep.
- ui-message.ts: TeacherUITools entries for the four tools (mechanical).
- tests: fs-tools suite (glob semantics, pi formats, exclusions, limits),
  registry/card renders, shared-fragment composition pins, tool-registry
  key updates, read re-anchor.

src/agent/prompts/shared/05-learner-files.md

@@ -0,0 +1,14 @@
+## Learner files
+
+The learner's files live on his machine. He references them in messages — by full path,
+by name, or by description ("my calculus notes"). Locating and reading them is your job;
+never ask him to paste file contents into the chat.
+
+- Paths resolve against the learner's home directory: relative paths and omitted search
+  roots mean "somewhere in the home directory".
+- The learner may name a file without saying where it is: find it yourself with `find`
+  (glob by filename) or narrow with `ls` before reading. A distinctive name is enough.
+- `grep` searches file contents across a directory — use it when the file is found but
+  the right passage isn't, or to locate material by phrase.
+- Read what you locate with `read` (text in slices, images as attachments). These tools
+  are read-only: you cannot and should not modify anything on his machine.