refactor: unify upload UX across GameDetails subtabs

[zurdi15]

Description
^{Explain the changes or enhancements you are proposing with this pull request.}

Stacked on top of #3569. Aligns every upload affordance in the GameDetails view with the layout pioneered by ScreenshotsSubtab: the sidebar becomes navigation-only and each panel grows a section header at the top whose right-hand cluster hosts the contextual actions (Upload, mainly).

Touched subtabs:

• SaveDataTab (Saves + States) — Upload moved into each Mine section header. Sidebar drops the RCollapsible action panel.
• MediaTab Manual — sidebar action panel removed. Header keeps the entry selector (when 2+ manuals coexist) + Upload only. Delete and Redownload migrate into the PDF viewer's toolbar via new PdfViewer props (deletable, redownloadable, redownloading) and emits (delete, redownload) — they read as one action cluster next to Download.
• MediaTab Soundtrack — header with just Upload; same sidebar cleanup.
• MediaTab subtab order — Screenshots now sits above Soundtrack (Manual → Screenshots → Soundtrack).
• FilesTab — sidebar action panel gone. Header keeps Upload only (the previous Download all / Copy link are reachable via select-all + the existing selection toolbar). The disabled-with-tooltip Upload behaviour for non-manual/soundtrack folders is preserved.
• ScreenshotsSubtab + SaveDataTab — drop the redundant "Private to you until you make them public" subtitle and its 17-locale key (screenshots-section-mine-desc).

Entrance animation:

• New r-v2-asset-fade CSS (320ms, 14px rise + fade, no scale, no overshoot, 24ms stagger) sits next to the existing r-v2-card-fade so dense info rows have their own visual vocabulary distinct from hero cards.
• Applied to AssetList rows, AssetStrip tiles, FileRow, screenshot thumbnails, and soundtrack track rows.

Checklist
^{Please check all that apply.}

• I've tested the changes locally
• I've updated relevant comments
• I've assigned reviewers for this PR
• I've added unit tests that cover the changes

Screenshots (if applicable)

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[Copilot]

Pull request overview

Refactors the v2 GameDetails “upload” experience so contextual actions live in each panel’s section header (sidebar becomes navigation-only), and introduces a lighter-weight “asset row/tile” entrance animation distinct from the existing card reveal.

Changes:

• Added r-v2-asset-fade global animation and applied it across asset rows/tiles (lists, strips, file rows, screenshots, soundtrack rows).
• Migrated multiple GameDetails subtabs (SaveData, Media, Files) away from sidebar action panels to header-based actions; reordered Media subtabs (Manual → Screenshots → Soundtrack).
• Extended PdfViewer with optional delete / redownload controls so manual actions can live in the viewer toolbar.

Reviewed changes

Copilot reviewed 28 out of 28 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
frontend/src/v2/styles/global.css	Adds the new r-v2-asset-fade animation and reduced-motion variant.
frontend/src/v2/components/shared/AssetStrip.vue	Applies r-v2-asset-fade with stagger index to strip tiles.
frontend/src/v2/components/shared/AssetList.vue	Applies r-v2-asset-fade with stagger index to list rows.
frontend/src/v2/components/GameDetails/SoundtrackPanel.vue	Animates soundtrack track rows via r-v2-asset-fade.
frontend/src/v2/components/GameDetails/ScreenshotsTab.vue	Animates screenshot thumbnail cells via r-v2-asset-fade.
frontend/src/v2/components/GameDetails/ScreenshotsSubtab.vue	Removes the “mine” subtitle line using the deleted locale key.
frontend/src/v2/components/GameDetails/SaveDataTab.vue	Removes sidebar action panel; moves Upload into Mine section headers for Saves/States.
frontend/src/v2/components/GameDetails/PdfViewer.vue	Adds optional deletable / redownloadable / redownloading props and emits for toolbar actions.
frontend/src/v2/components/GameDetails/MediaTab.vue	Removes sidebar action panel; introduces per-panel headers; reorders subtabs; wires PdfViewer delete/redownload.
frontend/src/v2/components/GameDetails/FilesTab/FilesTab.vue	Removes sidebar action panel; adds header Upload (with existing disabled+tooltip behavior) and animates FileRow items.
frontend/src/v2/components/GameDetails/FilesTab/FileRow.vue	Forwards $attrs onto the root <li> so parent-provided animation class/style can apply.
frontend/src/locales/zh_TW/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/zh_CN/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/ru_RU/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/ro_RO/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/pt_BR/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/pl_PL/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/ko_KR/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/ja_JP/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/it_IT/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/hu_HU/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/fr_FR/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/es_ES/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/en_US/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/en_GB/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/de_DE/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/cs_CZ/rom.json	Removes screenshots-section-mine-desc translation key.
frontend/src/locales/bg_BG/rom.json	Removes screenshots-section-mine-desc translation key.

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