refactor: changed effects, add shell completions

- Extract all apply_* effect methods from screenshot.rs into dedicated
  src/effects.rs (blur, vignette, pixelate, swirl) — screenshot.rs
- Rewrite apply_blur: replace broken fastblur::gaussian_blur (horizontal-
  only box blur, backbuf dropped) with correct inline two-pass sliding-
  window box blur operating directly on Cairo surface bytes — ~10×
  faster, no ImageBuffer round-trip, no fastblur dependency
- Remove melting effect entirely (seems to be hard to implement
  properely, tried multiple itterations)
- Drop unused dependencies: fastblur, rand
- Add clap_complete dependency + --completions {bash,fish,zsh} flag,
  with CompletionShell enum in config.rs
- Fix show_* flags defaulting to true: remove default_value_t=true from
  show_media, show_battery, show_network, show_bluetooth, show_album_art,
  show_caps_lock_text — all now opt-in (matching user expectation)
- Convert peek toggle to hold: toggle_peek() → set_peek_held(held: bool),
  Press calls set_peek_held(true), new Release handler iterates all
  surfaces and calls set_peek_held(false), matching Ctrl-hold behavior
- Fix cursor rendering: increase font size 11→14 for peeked chars,
  handle cursor_position == 0 (prevent negative t wrapping to far ring
  end)
- Fix peek hit-test: use shape-aware point_in_shape() instead of simple
  circle pill/square/diamond/hexagon now detect clicks correctly within
  their area
- Remove per-frame DEBUG logs: PEEK/DOT mode in lock.rs,
  set_password_display/peek_password in render/mod.rs
- Update README: embed rustlock-effects.webp demo, remove melting
  references, correct show_* defaults and options table

Cargo.toml

@@ -16,6 +16,7 @@ cairo-rs = { version = "0.20", default-features = false, features = ["png"] }
 gdk-pixbuf = { version = "0.20", default-features = false, features = ["v2_40"] }
 pangocairo = { version = "0.20" }
 clap = { version = "4.6", default-features = false, features = ["derive", "std", "help", "usage", "error-context"] }
+clap_complete = { version = "4.6", default-features = false }
 toml = { version = "1.1", default-features = false, features = ["parse", "display", "serde"] }
 serde = { version = "1.0", default-features = false, features = ["derive", "std"] }
 zeroize = "1.8"
@@ -25,11 +26,9 @@ whoami = "1.6"
 zbus = { version = "5.14", default-features = false, features = ["tokio"] }
 mpris = "2.0"
 tokio = { version = "1.51", default-features = false, features = ["rt", "rt-multi-thread", "macros", "time", "sync"] }
-rand = { version = "0.10" }
 reqwest = { version = "0.12", default-features = false, features = ["blocking", "rustls-tls"], optional = true }
 image = { version = "0.25", default-features = false, features = ["png", "jpeg"] }
-    fastblur = "0.1"
-    pam-client = "0.5"
+pam-client = "0.5"
     calloop = "0.13"
     xkbcommon = "0.7"
     calloop-wayland-source = "0.3"