Bring README and TODO.md in line with next after the milestone merge (closes #132)

Docs only. TODO.md's Next Step no longer says open issues wait on
`next`: no implementation work is open, and the cache design waits on
sneak's review. The README is corrected where the code contradicts it:
where SRP lives and how the login subkey is derived, when email OTP is
used, how the auth token is encoded, the download retry's temporary
files, which CLI commands open a library, what `--exif` records, the ML
data fetch during `quak backup`, the default cache directory, and the
`408`/`429` retries.

Model: opus-5-5

README.md

@@ -399,11 +399,11 @@ download layer rather than in `ApiClient`, and that is the common failure for
 multi-megabyte photos over a CDN. The secretstream pull state is not resumable
 and these endpoints have no Range support, so a retry starts the file over. The
 atomic write is part of the retried unit: each attempt writes its own temporary
-files, one for most files and two for a live photo (its image and its video),
-and removes them if it fails. Only the attempt that completes renames anything
-into place. `runBackup` and `runMetadataBackup` are unchanged: the retry sits
-below them, and a file that fails after exhausting it is still logged, counted,
-and stepped over.
+file and removes it if the attempt fails, and only the attempt that completes
+renames its file into place, so a download that needed three attempts still
+performs exactly one rename. `runBackup` and `runMetadataBackup` are unchanged:
+the retry sits below them, and a file that fails after exhausting it is still
+logged, counted, and stepped over.
 
 One imprecision is deliberate and worth knowing about. When a body ends part-way
 through a secretstream chunk, Poly1305 fails and carries no framing signal, so a
@@ -452,18 +452,18 @@ thumbnails), for the user to delete if they want it gone.
 ### CLI surface
 
 ```
-quak [--cache-dir <path>] <command>                       global: local metadata/content cache location
-quak login                                                interactive or QUAK_EMAIL/QUAK_PASSWORD
-quak whoami                                               print logged-in account as JSON
-quak logout                                               end the session, delete it
-quak collections [--json]                                 list all collections
-quak files --collection <id> [--json]                     list files in a collection
-quak get <fileID> [--out path] [--collection]             download and decrypt a file
-quak get-thumb <fileID> [--out] [--collection]            download and decrypt a thumbnail
-quak backup <dir> [--json]                                full incremental backup
-quak backup-metadata <dir> [--exif]                       dump all decrypted metadata as JSON
-quak helper list-missing-thumbnails [--json]              find files with missing thumbnails
-quak helper fix-missing-thumbnails [--file ids] [--json]  generate + upload missing thumbnails
+quak [--cache-dir <path>] <command>             global: local metadata/content cache location
+quak login                                      interactive or QUAK_EMAIL/QUAK_PASSWORD
+quak whoami                                     print logged-in account as JSON
+quak logout                                     end the session, delete it
+quak collections [--json]                       list all collections
+quak files --collection <id> [--json]           list files in a collection
+quak get <fileID> [--out path] [--collection]   download and decrypt a file
+quak get-thumb <fileID> [--out] [--collection]  download and decrypt a thumbnail
+quak backup <dir> [--json]                      full incremental backup
+quak backup-metadata <dir> [--exif]             dump all decrypted metadata as JSON
+quak helper list-missing-thumbnails [--json]    find files with missing thumbnails
+quak helper fix-missing-thumbnails [--file ids] generate + upload missing thumbnails
 ```
 
 Every command except `login`, `whoami` and `logout` runs on the cache-backed
@@ -483,8 +483,7 @@ Ente's clients name them (`IMG_0001.heic` and `IMG_0001.mov`). With
 `PATH`'s name and the video's extension; a `PATH` with the video's extension is
 refused. `backup-metadata --exif` (alias `--all`) additionally fetches each
 file's original through the cache and records its XMP metadata and, for a JPEG,
-its EXIF metadata and dimensions. `collections`, `files`, `backup`,
-`helper list-missing-thumbnails` and `helper fix-missing-thumbnails` take
+its EXIF metadata and dimensions. The listing and backup commands support
 `--json` for machine-readable output.
 
 `backup-metadata` fetches ML data in requests of up to 200 files. When a request

TODO.md

@@ -29,12 +29,11 @@ declares one.
   the SRP handshake uses `fast-srp-hap`, outside `crypto/`; the SRP password is
   the first 16 bytes of a 32-byte subkey; email OTP replaces SRP when the
   account has email MFA on; the auth token is sent as URL-safe base64 with
-  padding; each download attempt writes its own temporary files, two for a live
-  photo, and only the attempt that completes renames them into place; `login`,
+  padding; each download attempt writes its own temporary file; `login`,
   `whoami` and `logout` open no library; `--exif` records XMP and, for a JPEG,
-  EXIF, and no IPTC; which commands take `--json`; `quak backup` still fetches
-  ML data; the default cache directory is the per-user one, not an XDG path on
-  macOS; and `408` and `429` are retried.
+  EXIF, and no IPTC; `quak backup` still fetches ML data; the default cache
+  directory is the per-user one, not an XDG path on macOS; and `408` and `429`
+  are retried.
 
 - 2026-09-28: Tested the live-photo writer's fsyncs (issue 130). A test checks
   that the image's and the video's temp files are fsynced before either is