[machado144]

Stacked on #32 (base release/v0.1.7).

Why

A hotkey another program already owns silently did nothing. On Windows, NVIDIA's overlay holds Ctrl+Alt+M (the practice key): snowlearner logged Hotkey unavailable to a file nobody reads, and every hint on screen kept saying "press Ctrl+Alt+M". The only fix was editing config.toml by hand and restarting.

What

• New TECLAS / KEYS tab in the panel, one row per hotkey (practice, recap, panel, magic hand, progress). ← → or Enter's list move it to any letter or digit under the modifiers it already has (Ctrl+Alt by default; modifiers written in config.toml are kept). A key another snowlearner action holds is never offered.
• Applied at once: Hotkeys::rebind releases the old set and registers the new one, no restart. Where the desktop owns the shortcuts (GNOME on Wayland), they are reinstalled; on other Wayland desktops a toast says to run snowlearner setup.
• A taken hotkey is visible: marked (in use) in its row and in the list, said in a toast when picked, and said at startup instead of the welcome.
• Every hint follows the change: the warrior's tips ("Press … and say a phrase"), the lesson footers, the idle nudge and the shortcut sheet all read the new keys right away.
• Every new string in lang/text.rs, pt-BR and English. No new dependency.

Not in this PR: capturing an arbitrary combination by pressing it. The rows pick the key; other modifiers still come from config.toml.

Tests

• Menu: a row changes the key and keeps its modifiers; a key another action holds is skipped by the arrows and absent from the list (32 options); a taken combination is marked in the row and in the list, in both languages; the tab cycles and clicks; the new rows and the help fit the panel; all five rows open a list like every other choice row.
• Hotkeys: the action that lost its key is named; every letter and digit parses.
• Against the real Windows API (one-off probe, not committed): registering Ctrl+Alt+Y + Ctrl+Alt+M reported M as taken (NVIDIA's overlay has it on this machine); after rebind to U, another manager could take Y and could not take U.
• cargo fmt --check, cargo clippy --all-targets -- -D warnings (default features and --no-default-features) clean. cargo test on Windows: 513 lib + 26 CLI pass.

Two lib tests fail on Windows only, both unrelated and failing without this PR's code paths: command_engine_passes_text_on_stdin_when_not_in_the_template (calls tee) and, intermittently, a_foreign_program_on_the_port_is_detected (its fake server closes the socket before the client reads; passes when run alone).

Not verified: clicking through the tab in the running app, the GNOME reinstall path, macOS.

Closes #31

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