chore: add Dockerfile, docker-compose, and Docker hosting docs (#12)

* chore: add Dockerfile, docker-compose, and Docker docs

- Multi-stage Dockerfile: Rust builder stage + debian:bookworm-slim runtime
  with Chromium, Node/single-file-cli, Python venv (yt-dlp + twitter-api-client)
- docker-compose.yml: wires ARCHIVR_BIND, config volume, and persistent data volume
- docker/config.example.toml: annotated TOML template for Docker deployments
- docs/README.md: add Hosting with Docker section; add ARCHIVR_BIND and
  ARCHIVR_STATIC_DIR to the Environment Variables reference

* fix: address code review issues with Docker setup

- .gitignore: whitelist Dockerfile, docker-compose.yml, docker/ so they
  are actually tracked (the * catch-all was silently dropping them)
- Dockerfile: build and ship the archivr CLI alongside archivr-server so
  users can run `archivr init` inside the container on first setup
- docker/config.example.toml: fix archive_path to point at the .archivr
  subdirectory that archivr init creates (not the parent directory), which
  is what read_archive_paths expects
- docs/README.md: replace the bare mkdir quickstart step with
  `archivr init`, explain why mkdir is insufficient; add a callout that
  auth_db_path must be set explicitly to a writable path when the config
  mount is read-only

* fix: address second round of Docker review issues

Chromium sandbox (P2):
- singlefile.rs: add ARCHIVR_CHROME_ARGS env var (space-separated flags
  appended to Chromium's --browser-args JSON array); Dockerfile sets it
  to --no-sandbox because Chromium refuses to start as root without it

Store-path outside volume (P1):
- README: pass explicit absolute store-path as the second positional arg
  to `archivr init` so the blob store lands on /data instead of the
  container layer (CLI default is ./.archivr/store, resolved from cwd,
  which is / with no WORKDIR set)

ENTRYPOINT vs CMD (P2):
- Dockerfile: switch from ENTRYPOINT to CMD so `docker compose run
  archivr archivr init …` overrides the full command instead of being
  appended to the server invocation

ffmpeg missing (P2):
- Dockerfile: add ffmpeg to the apt-get install block (required by
  yt-dlp --merge-output-format mp4 for bestvideo+bestaudio streams)

Node version (P2):
- Dockerfile: replace Debian bookworm's nodejs (18.x) with Node 20 via
  the NodeSource setup script (single-file-cli declares engines.node >=20)

Build context secrets (P2):
- Add .dockerignore excluding config/ and docker/ from the build context
  so runtime secrets (e.g. twitter-cookies.txt) are never sent to the builder
- Whitelist .dockerignore in .gitignore

docs:
- README: document ARCHIVR_CHROME_ARGS in the Environment Variables section

* fix: third round of Docker review issues

Rust toolchain (P1):
- Dockerfile: bump builder from rust:1.87 to rust:1.88; time@0.3.51,
  time-core@0.1.9, and time-macros@0.2.30 (present in Cargo.lock) all
  require MSRV 1.88, so the real cargo build --release step was failing

single-file-cli wait mode (P2):
- singlefile.rs: replace --browser-wait-until=networkidle2 with
  networkAlmostIdle; the single-file-cli option only accepts
  InteractiveTime/networkIdle/networkAlmostIdle/load/domContentLoaded
  (verified in options.js); networkidle2 is a Puppeteer concept that the
  CLI does not recognise, causing silent fallback to the earliest state
  and incomplete captures. networkAlmostIdle is the closest equivalent
  (<=2 open connections, matching Puppeteer's networkidle2 semantics)

Build context size (P3):
- .dockerignore: add target/, frontend/node_modules/, frontend/dist/;
  these can reach 1.4G+ after a local dev build and are never read by
  the Dockerfile, so sending them to the builder wastes time and memory

crates/archivr-core/src/downloader/singlefile.rs

@@ -68,18 +68,30 @@ fn save_with(
     // without a writable user-data-dir. Using a subdirectory of temp_dir
     // keeps it isolated and it gets cleaned up with the rest of the temp dir.
     let chrome_data_dir = temp_dir.join("chrome-data");
-    let browser_args = format!(
-        "[\"--disable-web-security\",\"--user-data-dir={}\"]",
-        chrome_data_dir.display()
-    );
+    // Build the browser-args JSON array. Start with the flags always required,
+    // then append any extra flags from ARCHIVR_CHROME_ARGS (space-separated).
+    // Docker containers running as root need "--no-sandbox" here because
+    // Chromium refuses to start as root without it.
+    let mut chrome_flags = vec![
+        "--disable-web-security".to_string(),
+        format!("--user-data-dir={}", chrome_data_dir.display()),
+    ];
+    if let Ok(extra) = std::env::var("ARCHIVR_CHROME_ARGS") {
+        chrome_flags.extend(extra.split_whitespace().filter(|s| !s.is_empty()).map(str::to_string));
+    }
+    let quoted: Vec<String> = chrome_flags
+        .iter()
+        .map(|f| format!("\"{}\"", f.replace('\\', "\\\\").replace('"', "\\\"")))
+        .collect();
+    let browser_args = format!("[{}]", quoted.join(","));
 
     let out = Command::new(single_file)
         .arg(url)
         .arg(&out_file)
         .arg(format!("--browser-executable-path={chrome}"))
         .arg("--browser-headless")
-        .arg("--browser-wait-until=networkidle2")
-        // Extra delay after networkidle2: Cloudflare Fonts injects @font-face
+        .arg("--browser-wait-until=networkAlmostIdle")
+        // Extra delay after networkAlmostIdle: Cloudflare Fonts injects @font-face
         // CSS after HTML parse, so the font hook needs more time to see it.
         .arg("--browser-wait-delay=2000")
         // Realistic UA: some origins block headless Chrome's default UA string.