fix: Win11 focus border black color + packaging script resilience

[AgentX-asaf]

Summary

• Fix Win11 black focus border: The focused pane border rendered black on Windows 11 because the default accent color used an RGB variable from :root, which CEF's compositor fails to resolve on backdrop-filter elements. Agent colors (HEX inline styles) rendered correctly. Unified both paths into a single --block-focus-color inline style that always uses HEX.
• Fix packaging script MSYS2 regression: scripts/package-cef-portable.sh failed silently due to MSYS2 bash stdout FD corruption combined with set -euo pipefail. Dropped set -e, added resilient log()/die() helpers with explicit error checks.
• Fix powershell → pwsh: Changed PowerShell 5.1 call to PowerShell 7 per project rules.

Changes

File	Change
frontend/app/block/blockframe.tsx	Replaced --block-agent-color + has-agent-color class with unified --block-focus-color inline style
frontend/app/block/block.scss	Collapsed two CSS rules (agent color override + default) into single rule using var(--block-focus-color)
scripts/package-cef-portable.sh	Dropped set -e, added log()/die() helpers, explicit error checks, powershell → pwsh
Version files	Bumped to v0.33.44

Root cause

CEF on Windows 11 has a compositor bug where :root CSS custom properties containing RGB values render as black when applied to elements with backdrop-filter. The .block-mask element uses backdrop-filter: blur(0.1px) to force correct GPU compositing order above xterm's scroll layer. Agent-loaded terminals worked because their border color was set as an inline HEX style, bypassing the :root variable path entirely.

Test plan

• Launch portable build (v0.33.44 on Desktop)
• Open a standard terminal pane — focus border should be blue (#419FE0), not black
• Open an agent terminal (e.g., AgentX with red) — focus border should be red
• Verify unfocused panes still show dark border
• Run task cef:package:portable — should complete without silent failures

🤖 Generated with Claude Code

[reagentx-workflow]

ReAgent Diagnostics

Field	Value
ReAgent Version	5.12.5
Trigger	PR opened
Project Context	CLAUDE.md loaded
Model	claude-opus-4-6
Effort	high
Ref Repos	Disabled
Merge Analysis	1 regression(s) detected
Review Time	29.6s
Timestamp	2026-04-05T08:08:55Z
Repository	agentmuxai/agentmux
PR	#300

---

Issues:

• package.json:9 - Version downgrade detected: main is at 0.33.45 but this PR sets 0.33.44. Rebase on latest main and bump to 0.33.46
• frontend/app/block/blockframe.tsx:710 - Hardcoded fallback color #419FE0 — if the accent color theme changes, this won't update. Consider reading the resolved HEX value from the theme at runtime instead of hardcoding

[reagentx-workflow]

ReAgent Diagnostics

Field	Value
ReAgent Version	5.12.5
Trigger	Re-review (new commits)
Project Context	CLAUDE.md loaded
Model	claude-opus-4-6
Effort	high
Ref Repos	Disabled
Merge Analysis	1 regression(s) detected
Review Time	57.0s
Timestamp	2026-04-05T15:26:46Z
Repository	agentmuxai/agentmux
PR	#300

---

Issues:

• package.json:9 - Version downgrade: main is at 0.33.45 but this PR sets 0.33.44 (which already exists in main history at commit bfa5c81). Rebase on latest main and bump to 0.33.46
• frontend/app/block/blockframe.tsx:561 - Hardcoded fallback #419FE0 (duplicated at line 750) won't track theme changes to --accent-color defined in theme.scss:14. Read the computed HEX value from the DOM at runtime instead of hardcoding

[reagentx-workflow]

ReAgent Diagnostics

Field	Value
ReAgent Version	5.12.5
Trigger	Re-review (new commits)
Project Context	CLAUDE.md loaded
Model	claude-opus-4-6
Effort	high
Ref Repos	Disabled
Merge Analysis	1 regression(s) detected
Review Time	58.7s
Timestamp	2026-04-05T15:33:32Z
Repository	agentmuxai/agentmux
PR	#300

---

Issues:

• package.json:9 - Version downgrade: main is at 0.33.45 but this PR sets 0.33.44 (0.33.44 already exists in main at commit bfa5c81). Rebase on latest main and bump to 0.33.46
• frontend/app/block/blockframe.tsx:561 - Hardcoded fallback #419FE0 (duplicated at line 750) will drift if --accent-color in theme.scss:14 is changed. Use getComputedStyle(document.documentElement).getPropertyValue('--accent-color') resolved to HEX via colord (already a dependency) instead of hardcoding