The file field in the start-block input format only offered a raw JSON
editor expecting hand-written base64 objects, which users routinely
filled with junk (local paths, raw text, leftover placeholders) and
which never actually fed a run.

Reuse the existing FileUpload component for file-typed fields:
- Add an opt-in controlled mode (value/onValueChange) to FileUpload so it
  can be embedded where the value lives outside a subblock; store-bound
  consumers (stt/vision/agent) are unchanged.
- Render the uploader for file fields, with a toggle to fall back to the
  raw JSON editor for power users / legacy values.
- Detect file fields by normalized type (file[]/files/file/image) so
  copilot/API-authored variants render correctly too.
- Wire editor-attached files (already uploaded, run-ready) into manual
  runs via the executor's files channel; chat/API runs still override.

Backwards compatible: the inputFormat array shape is unchanged (file
values are stored as a JSON string of run-ready file objects); legacy
free-form values open in JSON mode so nothing is lost.

…r, harden types

Follow-up cleanup from /simplify + /cleanup review:
- Extract pure file adapters into input-format-files.ts (filesToControlValue,
  controlValueToFiles, serializeInputFormatFiles, defaultFileFieldMode) so they
  are unit-tested without a DOM; add tests.
- Derive InputFormatFile from the canonical executor UserFile so the editor and
  runtime file shapes can't drift.
- Consolidate the two manual run-input builders into one buildInputFormatInput
  helper so manual run and run-from-block handle files identically.
- Narrow file-field detection to the canonical file[] (matches the field-type
  dropdown and the existing execution/webhook file paths) so no pre-existing
  non-file[] field changes behavior.
- defaultFileFieldMode parses once; the file value is only parsed in upload mode.
- Add lib/component unit tests (45 passing).

…files input

Addresses review (Greptile P1s):
- parseInputFormatFiles now requires the full run-ready shape (id/name/url +
  finite size + type), so a partial file can't open in uploader mode or reach
  workflowInput.files only to be rejected by normalizeStartFile (which would
  silently drop every file).
- buildInputFormatInput no longer overwrites a user field literally named
  'files' with the upload channel; that reserved-name collision is left for the
  executor to surface.

…N mode

Addresses review round 2 (Greptile P1 + Cursor):
- parseInputFormatFiles now requires a non-empty key (the uploader always sets
  one); an external/signed URL with no recoverable key no longer opens uploader
  mode or reaches workflowInput.files only to be rejected.
- defaultFileFieldMode uses the uploader only when EVERY entry is run-ready;
  a mixed array with any legacy/partial entry stays in JSON mode so the uploader
  can't drop the entries it can't represent on the next save.

…ss values

Addresses review round 3 (Greptile P1 + Cursor):
- parseInputFormatFiles accepts a key-less file when its url is an internal
  /api/files/serve/... url (the executor recovers the key from it, same as
  normalizeStartFile); only a missing key with a non-internal url is rejected.
- The file field offers the uploader only when it can represent the stored
  value losslessly (empty or all run-ready); for mixed/legacy values it forces
  JSON mode and hides the toggle, so a sticky 'upload' preference can no longer
  drop entries the uploader cannot show on save.

…rmatFiles

Addresses review round 4 (Greptile): normalizeStartFile rejects falsy
id/name/url/type and file normalization is all-or-nothing, so an empty-string
field (e.g. hand-edited value with an empty id + internal url) would open in
uploader mode and drop every file from the run. Require non-empty strings to
match the executor.

…rnalFileUrl

Addresses review round 5 (Greptile): isInternalFileUrl only checks the URL
prefix, but the executor parses+decodes the key. A malformed internal URL (no
extractable key) passed the prefix check, got collected into workflowInput.files,
then normalizeStartFile rejected it and dropped the whole files array. Now mirror
the executor exactly — attempt parseInternalFileUrl and require a real key.
Tests use a realistic recoverable internal URL.

Addresses review round 6 (Greptile): files is NOT in the executor's reserved
input-format names (EXECUTION_CONTROL_OUTPUT_FIELD_NAMES), so the previous guard
silently dropped uploaded file[] values whenever a plain field named files
coexisted. files is the start block's canonical file channel (the chat trigger
names its own file field files), so uploaded files now always populate it and
take precedence — dropping real attachments is the worse outcome, and making
files a reserved-name error isn't viable since it's the legitimate file-field
name.