design(ui): refresh Activity layout and align theme colors

[domcyrus]

Activity's bars used colours that differed from traffic labels and Graph, and the repeated charts made the view harder to scan. This refresh gives Activity a clearer hierarchy and uses each theme's traffic colours consistently.

• Preserve the default TX blue / RX green convention; other presets and custom overrides keep their own traffic tokens.
• Add restrained RGB gradients ending at the direction token, with textured block shading for ANSI themes and fractional bar tips.
• Use paired traffic summaries, a roomier process ranking with neutral process names, and a capture coverage / attribution / interface sidebar on wide terminals.
• Remove the duplicate process-share chart and keep share bars beneath process names on compact terminals.
• Align Graph labels and default waves with the corresponding traffic tokens, preserving explicit wave overrides.
• Polish shared section rules, table headings, and responsive numbered tab navigation.

Previews

These are actual Ratatui TestBackend renders with seeded sample traffic and a reference terminal palette. ANSI shades depend on the terminal. Catppuccin retains its existing TX green / RX cyan mapping.

Default:

Catppuccin:

Compact preview · Tokyo Night preview

Validation

• Passed cargo fmt --all -- --check.
• Passed cargo clippy --all-targets --all-features -- -D warnings.
• Passed cargo test --all-features: 347 unit tests and 3 integration tests.
• Updated and reviewed Activity layout snapshots and rendered previews.
• Verified that the uploaded Git tree exactly matches the locally tested commit.
• Dependencies and lockfile are unchanged from the earlier successful dependency audit.

Still to resolve

The local cargo build --release failed at linking with unresolved ratatui_core symbols, including after rebuilding that dependency. The cause is unconfirmed; release validation must pass before merge.

An earlier full workspace run encountered 11 Linux process-attribution failures that also reproduced on the unchanged base in this environment. This revision reran the application suite, not that full workspace check. No host, capture, or core code changed.

Keeping this PR in draft for design review and release-build validation.