feat(frontend): dark-tech UI polish + map/local-view aspect improvements

[xiaolefang-dm]

Summary

This PR extends xiaole/fix/camera-cover-fit with a full frontend visual polish and layout fixes for better usability and consistency.

Included changes

1. Keep camera preview fill behavior

   • Uses BoxFit.cover to make camera preview fill its panel cleanly.

2. Fix local planning view stretching

   • In _LocalPlanningView, remove forced aspectRatio: 1.0.
   • Use grid-based ratio (gridInfo.width / gridInfo.height) when available.
   • Fallback to 1.0 only when grid data is unavailable.
   • Result: local map + overlays no longer look distorted.

3. Web viewport layout strategy (portrait vs landscape)

   • Portrait (aspect < 1): keep default stretch/fill behavior.
   • Landscape (aspect >= 1): lock app content to 1:1, top-aligned.
   • Improves visual stability on wider screens.

4. Dark-tech UI style refresh

   • Applied dark theme tuning in main.dart and home/device/operate related pages.
   • Improved card hierarchy, typography contrast, and panel readability.
   • Updated Device tab readability (especially Sensor mode and System metric rows).

5. Home page color unification

   • Reworked mixed gray/blue/green accents for Device/Map/Operate cards and Quick Status.
   • Use a more unified accent style to avoid visual mismatch.

---

Validation

• Ran flutter analyze on modified frontend files (no blocking errors).
• Ran flutter build web successfully after updates.

Note: existing non-blocking warnings (e.g. deprecations like withOpacity) are pre-existing/style-level and not runtime blockers.

---

Offline web resource support

This PR also removes runtime internet dependencies for the Flutter web app:

• Serves Flutter CanvasKit from the local web build instead of www.gstatic.com
• Serves fallback fonts locally instead of fonts.gstatic.com
• Replaces invalid local Roboto font files with real bundled font assets
• Documents building web with --no-web-resources-cdn

This makes the app safer to use in offline robot deployment environments.

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.17 s (252.9 files/s, 37191.0 lines/s)

Language	files	blank	comment	code
Python	13	613	262	3399
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	30	29	191
JSON	2	8	0	58
TOML	1	4	0	57
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	933	359	4884

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.13 s (315.8 files/s, 46444.8 lines/s)

Language	files	blank	comment	code
Python	13	613	262	3399
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	30	29	191
JSON	2	8	0	58
TOML	1	4	0	57
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	933	359	4884

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.20 s (211.6 files/s, 31701.4 lines/s)

Language	files	blank	comment	code
Python	13	624	273	3493
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	30	29	191
JSON	2	8	0	58
TOML	1	4	0	57
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	944	370	4978

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.18 s (238.4 files/s, 35051.7 lines/s)

Language	files	blank	comment	code
Python	13	613	262	3399
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	30	29	191
JSON	2	8	0	58
TOML	1	4	0	57
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	933	359	4884

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.18 s (230.3 files/s, 34019.9 lines/s)

Language	files	blank	comment	code
Python	13	615	262	3414
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	31	30	200
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	936	360	4909

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.17 s (243.4 files/s, 35963.5 lines/s)

Language	files	blank	comment	code
Python	13	615	262	3414
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	31	30	200
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	936	360	4909

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.18 s (238.6 files/s, 35570.8 lines/s)

Language	files	blank	comment	code
Python	13	620	262	3464
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	31	30	202
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	941	360	4961