docs: record manual test pass of auth and encrypted URL flows (closes #49) (#50)

closes #49

Records the P0 manual test pass in `TODO.md` per its Workflow section
(checked-off results into Completed Steps; cache size management and
eviction promoted to Next Step). `TODO.md` is the only changed file —
no production code changes, as the issue requires.

## Test setup

`pixad` built from `main` at `6573b9d` via `make build`, run on port
18099 with a throwaway local config (temp state dir, known
`signing_key`, `allowlist_hosts` including `s3.sneak.cloud`), driven
with curl using explicit cookie replay (session cookies are
`Secure`/`HttpOnly`/`SameSite=Strict`).

## Results — all six checks PASS

1. **Login form**: GET `/` → HTTP 200, `Pixa - Login` page with
   `name="key"` password form.
2. **Wrong key error**: POST `/` with `key=wrong-key` → HTTP 200 login
   page containing "Invalid signing key".
3. **Generator form**: POST `/` with the correct signing key → HTTP 303
   to `/` with `Set-Cookie: pixa_session=...; HttpOnly; Secure;
   SameSite=Strict`; GET `/` with that cookie → `Pixa - URL Generator`
   with the `/generate` form and logout link.
4. **Encrypted URL serves image**: POST `/generate` (ttl=3600) produced
   a `/v1/e/<token>/img.jpeg` URL → HTTP 200, `Content-Type:
   image/jpeg`, 800x600 baseline JPEG, 61706 bytes.
5. **Expired URL → 410**: a ttl=1 URL fetched after 3 s → HTTP 410 Gone
   with `{"error":"URL has expired","status":410,...}`.
6. **Logout**: GET `/logout` → HTTP 303 to `/` with `Set-Cookie:
   pixa_session=; Max-Age=0`; subsequent GET `/` → login form again.

Additionally, all nine checks in `scripts/manual-test.sh` passed
against the same server instance.

## Verification

`make check` green on the branch head (all tests, golangci-lint 0
issues, fmt-check clean) — the first fully green `make check` on a
`main`-derived branch under the current linter, confirming the #47/#48
fix on merged `main`.

Note for review: the test execution was performed this session; the
adversarial re-review (independently re-running the six flows) is still
pending and should happen before merge.

Co-authored-by: sneak <sneak@sneak.berlin>
Reviewed-on: #50
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

TODO.md

@@ -19,14 +19,34 @@ on main.
 
 # Next Step
 
-P0: manual test pass of the auth and encrypted URL flows, then commit
-the checked-off results to TODO.md: visit / and see the login form;
-wrong key shows an error; correct signing key shows the generator form;
-a generated encrypted URL serves the image; an expired URL (short TTL)
-returns 410; logout redirects back to login
+P0: implement cache size management and eviction so the disk cannot
+fill up
 
 # Completed Steps
 
+- 2026-08-07 manual test pass of the auth and encrypted URL flows
+  against a locally built and running `pixad` (built from `main` at
+  `6573b9d`, port 18099, local throwaway config); all six checks
+  passed, plus all nine tests in `scripts/manual-test.sh` (closes #49):
+    - [x] visit `/` and see the login form: HTTP 200, `Pixa - Login`
+      page with `name="key"` password form
+    - [x] wrong key shows an error: POST `/` with `key=wrong-key`
+      returned HTTP 200 login page containing "Invalid signing key"
+    - [x] correct signing key shows the generator form: POST `/`
+      returned HTTP 303 to `/` with
+      `Set-Cookie: pixa_session=...; HttpOnly; Secure; SameSite=Strict`;
+      GET `/` with that cookie rendered `Pixa - URL Generator` with the
+      `/generate` form and logout link
+    - [x] a generated encrypted URL serves the image: POST `/generate`
+      (ttl=3600) produced a `/v1/e/<token>/img.jpeg` URL that returned
+      HTTP 200, `Content-Type: image/jpeg`, an 800x600 baseline JPEG of
+      61706 bytes
+    - [x] an expired URL (short TTL) returns 410: a ttl=1 URL fetched
+      after 3 s returned HTTP 410 Gone with
+      `{"error":"URL has expired","status":410,...}`
+    - [x] logout redirects back to login: GET `/logout` returned HTTP
+      303 to `/` with `Set-Cookie: pixa_session=; Max-Age=0`;
+      subsequent GET `/` rendered the login form again
 - 2026-08-07 fix the two remaining gosec findings (G124 in
   internal/session): session cookies now always carry
   Secure/HttpOnly/SameSite=Strict on both the set and clear paths;
@@ -53,8 +73,6 @@ returns 410; logout redirects back to login
 
 # Future Steps
 
-- P0: implement cache size management and eviction so the disk cannot
-  fill up
 - P0: validate configuration on startup, fail fast on bad config
 - P1: implement blocked networks configuration to extend SSRF
   protection