Minimize line - #1

* new remote file streaming API packets.  implemented 'stat' for remote files

* introduce filedata packets.  allow streaming RPCs.  fix RPC bug with combined packet parsers.  implement file streaming for filestream RPC.

* checkpoint on adding write-file

* completely untested write-file impl -- writefilecontext, condition var for signaling new data packets, cleanup goroutine, ready/done states.

* better error messages, also unlock MServer before calling done on wfcs

* fix bug with perm json tag.  change constant name

* RPC for remote file streaming -- just implemented 'stat' for now (streaming to come)

* allow RPC iterators for MShell RPCs.  implement two test commands to test viewing files

* implement read-file handler

* read-file: allow overriding of content-type and use line's cwd not remote instance cwd

* checkpoint on write-file impl

* implemented metacommand version of write file

* checkpoint, untested write-file impl

* multipart handling for write-file data

* add usetemp param to writefile

blockstore progress

Work through docs/open-issues.md; wavetermdev#5 deferred (documented blocker).

wavetermdev#1 gitattributes merge=union for the three generated wshrpc client files
   (wshclient.go, wshclientapi.ts, gotypes.d.ts); tsgen guards backstop a bad union.

wavetermdev#2 split two agent-view god-files (move-only, call sites unchanged):
   - runbody.tsx 881->561: card family -> runcards.tsx, plan editor -> planpreview.tsx
   - agentsviewmodel.ts 1030->895: grid geometry -> cardgridlayout.ts (+ tests),
     re-exported so importers are untouched.

wavetermdev#3 (3a) transcript-stream per-card unmount watcher leak:
   - server cancelRequest now cancels the request context (not just the bool), so a
     streaming handler's goroutine + fsnotify watcher unwind while the link is up.
   - client emits the wire cancel synchronously from an overridden return() in
     sendRpcCommand -- gen.return() hangs and never runs finally when the generator is
     parked at the never-settling await (a quiet stream), so a finally-based cancel
     would be missed. Guarded by go -race + client vitest.
   - 3b (stateful projection) intentionally not built (measure-first).

wavetermdev#4 channel-attachment temp-file cleanup: WriteTempFileCommand now uses a distinct
   waveterm-attach- prefix (the bare waveterm- sweep could delete /tmp/waveterm-<uid>
   socket dirs on Linux/macOS); SweepTempAttachments reaps dirs >24h, wired into
   wavesrv startup + a 4h loop.

Feature wavetermdev#1: open documents/images/code from outside the app (file association,
wave:// protocol, CLI, drop-on-block) into a new preview tab via a central emain
router with cold-start buffering + window:nativeopenhandler gate.

Feature wavetermdev#2: drag files between directory-preview blocks to copy/move -- same-tab,
cross-window (native uri-list bridge + emain drag broker), and local<->remote --
reusing existing FileCopy/FileMove RPCs.